Anime:
- Serial Experiments Lain (to this day, the single most engrossing, thought-provoking show, animated or not, that I've seen)
- Neon Genesis Evangelion
- FLCL
- Hellsing (horrible, I know)
- Cowboy Bebop
- Trigun
- And every once and a while, it's nice to watch an episode or two of "Super Milk-Chan: 100% Whole."
Manga:
- Hellsing
- FLCL
I wish I could find the Lain manga, but I haven't had any luck.
EDIT: Ah damn. I just had to add Cowboy Bebop and Trigun even though I said the three-five thing was a good idea. They're too good to leave out... CB especially.