I have a lot of favorites, and I can't really pick a favorite. I'm just not good at doing that, lol. Anyway, here goes nothing:
Aria (the entire series)
Boku wa Tomodachi ga Sukunai
Elfen Lied
High School DxD
K-ON!
Kara no Kyoukai (all seven movies)
Neon Genesis Evangelion
Spice and Wolf
Seitokai Yakuindomo
Shiki
Shinsekai Yori
Yuyushiki
Just for the hell of it, I'll list some hentai that I love to death too:
Kuroinu: Kedakaki Seijo wa Hakudaku ni Somaru
Bible Black
Bible Black: Only
Bible Black: Origins
Bible Black: New Testament
Kangoku Senkan
Anejiru 2
Oh, I forgot to add. I hate English dubs. I'd much prefer to read subtitles.