Plenty have been mentioned before, but I'll go ahead and name a few;
Death Note: Aside from it's own flaws (gets convoluted towards the end), it really is a really well done anime with just the right amount of pacing.
Code Geass: Again, it gets pretty convoluted at the end, but it's another really well done anime that I just love to watch.
FullMetal Alchemist: ONCE AGAIN, a bit convoluted at the end (see a pattern?) but not as much as the others, and it's extremely well paced with good action and animation. Some people prefer the manga/Brotherhood, but I prefer the original.
Cowboy Bepop: Not amazing for me, I only watched it on YouTube, but I can see why it's got a lot of love.
Naruto: Before Sasuke left the show, then it was just filler after filler of the same thing...
I need to watch more anime...
Apparently One Piece is good, but after 4Kids bastardization of the show I never watched it as I thought it was just like Naruto in the filler department only stupider and kiddier.