Getting into manga

[kasperbbs]

Since most of my favorites have already been mentioned then:

Noblesse - It's an action, comedy.. My English is too poor to make a proper description and its late, sorry, all i can say is that i loved every single one of these, oh and some of them are manhwa's.
Tower of god
Until death do us part
The Breaker
Vinland saga
Holyland
Blade of the immortal
Samurai Deeper Kyo

 

[carnege4]

Deadman Wonderland may be a good one for you.
But is not completed yet.

For action we have Berserk.

Franken Fran is another good one.
I wouldn't call it "action" i would call it "smart horror".
If you are expecting a description, just know this: There's NO WAY to describe this manga.

Still one of the best.

Franken Fran. Get ready to have your brain bleached though.

Mah nigga

 

[Jonluw]

Monster [http://myanimelist.net/manga/1/Monster] is a lot like Death note, genre wise. At least the two first issues are. I couldn't find the rest.

If you happen to be looking for something with more direct action, and less of a crime/mystery focus, read Vagabond [http://myanimelist.net/manga.php?id=656]. It's a seriously great series about the life of Miyamoto Musashi (a historical samurai).
A part that particularly stands out in my mind is the introduction of a deaf character. His story is told almost entirely without dialogue. Just page after page of fantastic art.
Oh, did I mention?

Spoiler: The art is fantastic. Particularly the parts with watercolours.

More notably, I'd recommend to stay away from the shonen series. Stuff like Naruto, One piece, Bleach, Dragon ball, etc. is in my opinion not really worth reading at all, but regardless of my opinion on their worth, they really aren't good for introducing you to the medium unless you're between 8-13 years of age.
Actually, just stay away from anything labeled 'shonen' to begin with if you want something mature.

Also, I wish to congratulate you on Death note as a choice of first manga. The beginning is pretty much unrivaled in its ability to hook the reader.
Around the middle of the story, it starts getting quite a bit worse though. Personally, I stopped reading the manga a bit into the last third. I watched the anime just to figure out how the story ended without having to make the effort to read it.

 

[Mordekaien]

Hellsing. This is how vampires are meant to be done.

Claymore. Hard to think of an explanation here but is quite good.

This. Hellsing is one of my all time favorites, with great art, characters and motherfucking badass vampires.

As for Claymore, it's basically Witcher in bikini with a slight twist.

Also, Berserk. Seriously go read Berserk.

 

[Mike Laserbeam]

Anything by Naoki Urasawa, he's simply the best manga mystery author out there. And one of the best mystery authors full stop. His manga will blow you away, I promise.
(Monster, 20th Century Boys, Pluto etc.)

Anything by Nobuyuki Fukumoto. His works are complete genius. Sure, the artwork is poor, but it fits the stories!
(Kaiji, Strongest Man Kurosawa, Zero etc.)

One Piece, FullMetal Alchemist, Kenichi: The Mightiest Disciple, Liar Game, Medaka Box, Akira, Dragonball, Mirai Nikki... uhh... I know I'll kick myself when I remember any I've forgotten.

Edit:
Bakuman! It could either serve as a good introduction into the world of manga, or be too confusing to read coming from nothing, as it's a story about the writing of manga.

 

[Queen Michael]

Lone Wolf and Cub is about an assasin in old Japan and his son. "Together, they walk the road to Hell." It's the second best manga I've ever read, and I've read about 520 different mangas. You've never seen so poetic and beautiful stories about murder.

I'm no authority on Manga, but I read Lone Wolf and Cub while I was practicing Iaido in my teens- very cool stories.

I also read some Battle Angel Alita - about a cyborg learning about her past, and the world she has forgotten, while perfecting her martial arts skills; and Domu, about a kid's life in an apartment block and an old man's secret. Very violent, that one.

Thanks for mentioning those two. I'd recommend them as well.

 

[niknar266]

If it's action ones you're looking for I think most people have suggested a lot of good ones to start with.
Hellsing, Berserk awesome and gory manga but I warn you Berserk is quite disturbing at times since you mention not liking d gray man for being twisted.
There is the mainstream shounen stuff Naruto, Bleach, One piece etc which normally is a good starting point till you decide whether go on to read more obscure stuff.
Someone mentioned Rave master and I recommend that as well good action and some goofy comedy. If you Like Rave Master I'd suggest Fairy Tail afterward it's done by the same author but you can tell his art and storytelling has improved a lot since Rave Master.

 

[Dimitriov]

Vagabond. By Takehiko Inoue.

It's a fictionalized account of Miyamoto Musashi's life.

It's beautifully drawn (aesthetically much closer to "western" style art than some other manga, which might be good as a starter).

And it has some great action and sword fighting.

 

[DAAANtheMAAAN]

Just from looking at my shelf...

Rurouni Kenshin - A action/romantic comedy set in Japan in the late 1800's.

Trigun - A sci-fi western that goes from funny and action packed to incredibly somber and action packed.

Air Gear - Fighting, comedy, roller blades. Need I say more? Rather fan-service heavy as well, if you're into that kinda thing.

Mega Man Megamix/Gigamix - If you like Mega Man at all, you'll really like these. The stories in them either expand upon the game's storylines or makes new ones of it's own. Either way, it's the best incarnation of Mega Man I've come across.

Battle Royale - If you like something darker and violent, you might like this. The series involves a class of high school kids who are forced to fight each other to the death.

Genshiken - A slice-of-life manga about a college club dedicated to nerd culture. Not action packed at all, but it's all very well written.

Cromartie High School - A comedy series about an average high school kid attending a school filled completely with delinquents. This one is so incredibly stupid. Really stupid. So stupid that it becomes really funny. There are clips of the anime online, so you're welcome to watch them to see if it's for you.

EDIT: I can't believe I forgot Fist of the North Star!
Fist of the North Star, to sum it up to an insulting degree, involves a kind of kung-fu Jesus who wanders a nuclear wasteland helping those in need and punching bad guys so until they explode! If you can track it down it's definitely worth a read.

 

[Noetherian]

It's been said a few times already, but I can't recommend Monster enough. It's one of the few my (non-manga-addicted) best friend has really loved, and both the manga and anime are top notch. There's compelling drama of a caliber I rarely encounter anywhere and a wide cast of supporting characters who really bring depth to the world and the main cast as they go through their own struggles. Also, it's about a well-meaning genius surgeon and a charismatic young serial killer chasing each other across the German countryside. What's not to love?

Speaking of Naoki Urasawa, I've also been reading Pluto, which is his take on the Astro Boy story. It hasn't grabbed me the way Monster did, but I think it could also be fun for someone just getting into the genre since it's a modern take on a really classic story.

Blade of the Immortal is one of my favorites for gorgeous art, although plot-wise it's much less tight than Urasawa's stuff. That said, Anotsu is a really interesting character.

I'll go ahead and second Battle Angel Alita and Rurouni Kenshin while I'm at it. Fullmetal Alchemist I liked better as an anime, but it's a good one too.

Unfortunately I'm not too well-versed in the newer stuff... although if you're feeling adventurous or just in the mood for something superficially silly, I did get really into Eyeshield 21 a few years back. Yes, it's a manga about (American) football, but sports manga are an experience all to themselves with a surprising amount of emotional depth and character growth-- although I suppose they can afford to put a lot of development into rivalries and side characters when they run 400+ issues!

For Death Note, by the by, I would actually recommend the anime over the manga just because the anime is a bit more polished-- the manga suffers a bit from having been written and marketed as a serial where the anime was produced with the endgame in mind and shortens some of the fillery bits. Either way, it's still a great story.

And one more thing... just since you brought up Y! The Last Man, which is one of my favorite comics. (Brian K. Vaughan is the man!) There's a series called Ooku that has a similar premise but takes place in feudal Japan. I had mixed feelings through the first volume, but the ending was a pleasant surprise that sold me on the book as a whole. I've been meaning to look into it more. You and your girlfriend might even enjoy reading that one together, if it turns out to be as good as I'm hoping.

Anyway, that's more than enough out of me; happy reading (and please do check out Monster)!

 

[TehCookie]

I don't have any specific suggestions but I'll leave this here http://www.mangaupdates.com/series.html?id=41. It's pretty much a manga database where you can look for something that interest you and several different ways to find similar manga. The recommendations are pretty off but if you search by categories/tags or by genre you can easily find something similar and interesting.

 

[SlaveNumber23]

The first manga I read was Bleach, I definitely recommend it and it will last you quite a while. Fullmetal Alchemist is great too but if you're going to watch the anime, make sure you watch Fullmetal Alchemist: Brotherhood and not the other anime series.

 

[Tippy]

Psssh all these mainstream suggestions (well, mainstream for manga anyway).

I'm going to suggest you something that is PACKED with action, humor, nutidity (don't take it in an immature sense) and gets straight to the point - Aiki.
To start you off: http://www.mangareader.net/159-10230-1/aiki/chapter-1.html

(you probably already know this but manga panels are read from right to left)

It avoids the cliche "main character starts off sucking toes, finds a new power/gimmick and becomes God-punchingly powerful by the end" and tries to approach things from a different direction.

There's something extremely addictive about the story, progression and the main character who happens to be a colossal jerk but also heart-warmingly charming in his own way. The facial expressions/reactions are the icing on the cake, most of them are sooooo hillarious.

Also don't get me wrong, most of the suggestions in this thread so far are mostly excellent manga. I just needed something to break away from the growing list of cliches and Aiki was it.

Manga is huge, huge world and lets just say that if we were to accumulate all the manga that came out of Japan, we'd have enough to fill a multiple libraries (not even kidding). It's like a goddamn ocean and western comics can't even hope to come close the volumes.

 

[Casual Shinji]

Franken Fran is another good one.
I wouldn't call it "action" i would call it "smart horror".
If you are expecting a description, just know this: There's NO WAY to describe this manga.

Still one of the best.

Franken Fran. Get ready to have your brain bleached though.

Mah nigga

I'm almost through volume 4, but unfortunately it hasn't been able to keep up the "fucked-upness" of the first volume.

Or maybe I've just gotten used to it.

 

[aceman67]

I'm really surprised that no one has suggested Neon Genesis Evangelion. This series (which is coming to a close this winter when Vol. 13 comes out) takes a vastly different story line from the Anime (on which this manga is based, I know, weird, normally the anime is based on the manga... go figure.)

The story is darker (didn't think that was possible when I picked up my first volume), Shinji has a spine, and Kaworu hates kittens.

Just like Evangelion is a must watch for fans of the Mecha/mind-bending persuasion, this is a must read for the same reason.

My next suggestion is a little more light hearted: Azumanga Daioh. This manga about the high-school experiences of a group of girls did something that I didn't expect: It made me cry (one of the final scenes where one of the characters says farewell to her teacher was very similar to how I said goodbye to my favorite teacher). Its a light hearted comedy and is a decent read (its also 4 volumes of 4-koma style, quick read).

My next suggestion is Kareshi Kanojo no Jijō (Kare Kano or His and Hers Circumstances). This love story about two high school students is a surprisingly deep story spanning 21 volumes. It covers subjects ranging from the deceptiveness of first impressions, peer-pressure, bullying, teen-pregnancy, child abandonment, and suicide.

If you were a fan of the anime, I will beat you with a stick if you don't read this manga, because the Anime story leaves off around Volume 7, so you have 14 volumes worth of story that you simply must read.

 

[Tohru_Readman]

I second Black Lagoon, Fullmetal Alchemist, Bleach and Azumanga Daioh all great series.

I would like to add:

-Saturn Apartments
-Zombie Loan
-Zombie Powder
-Sayonara, Zetsubou-Sensei
-Genkaku Picasso
-Durarara!!
-Yotsuba&!
-Solanin