on a slight detour...durarara is on netflix! (shame its just first season and not x2 as well)
Netflix's anime selection isn't actually too shabby given it's not targeted at it at all.
I find the big issue with anime and netflix is that their subtitles can often lag/break and entire sentences don't get subbed. It kinda kills the viewing experience having to rewind 2-3 times an episode to make a missing subtitle show up so you have a clue what is going on. If it's just grunting or screaming that's fine.
Moved to TV Shows as this is where anime-related discussion usually happens.
My answer is Death Note. Code Geass is not too far behind, though!
Death Note is my second best anime I ever watched. The best one is still Hellsing. It is not a big surprise that the latter named anime contains my favorite character: Alucard.