One Piece - If you have the patience for a slow, slow startup, I recommend this. It does fall into the average "Ah do anything fo' mah frenz" cliche's from time to time, but it has some pretty engaging storylines within and manages to avoid the my-power-level-is-bigger-than-yours pattern shonen anime usually follows (up until water 7 atleast).
FullMetal Alchemist - Seriously, if you haven't, watch it. Like now! Why are you still reading this? If you want manga to anime accuracy, pick FMA: Brotherhood. I'd personally suggest the original FMA though, mainly because Brotherhood tends to get kinda slow and overall I just like FMA's shift away from the original story alot better.
Gunslinger Girls - I just skimmed the thread mostly, so I don't know if this came up or not, but if not...why...? There's no real ending I can think of for the show, but the art is beautiful and the story itself is quite touching and tragic. Be warned though, the show is pretty slow, almost to the point where it's more like reading a book than watching a show.
seitokai yakuindomo - This show is like if a JP animation studio and Comedy Central somehow took on physical form and had dirty, dirty sex (which is fitting, given its subject matter). It's pretty damn hilarious and quite off-beat compared to other slice-of-life comedies I've seen.