I don't really watch much anime or read much manga anymore, but I still have a few favorites...
Anime: Death Note, Elfen Lied, Genshiken, Hellsing, Neon Genesis Evangelion, and Ouran High School Host Club.
Manga: Angel Sanctuary, Ayashi no Ceres, Count Cain, Fushigi Yugi, Godchild, Ouran...