Manga:
One Peice
Bleach
Hayate no Gotoku
Sora no Otoshimono (gotta get my ecchi XD)
Rosario + Vampire
Anime:
Sora no Otoshimono Forte
Clannad
Gundam 00
Hayate no Gotoku
Code Geass
These are just my current favorites though. If it was all time, FMA, DBZ, Fate/Stay Night, Toaru Majutsu no Index, Detective Conan, Melancholy of Haruhi Suzumiya, and Prince of Tennis would be up there too.