I have a rather small collection of manga that I had watched before...unfortunately,so I want to expand the list :P
Valkyrie Profile
Fate/Stay Night
Fate/Kaleid Liner Prisma Illya
Death Note
Tomoyo After ~Dear Shining Memories~
Shakugan no Shana
Pokemon Special/Adventures
Kanon
Air
Clannad
Fire Emblem
Brave Story
Hayate no Gotoku
.hack // series
Inuyasha
Bleach
Naruto
Witch Hunter
Final Fantasy XII
Full Metal Alchemist
20th Century Boys
21st Century Boys
Skip Beat
Onidere
Valkyrie Profile : Silmeria
Elfen Lied (Well..at least I can stand the gore of the manga version :P )
Shinigami no Ballad
Dance in the Vampire Bund
Shuffle Really! Really!?
Valkyrie Profile : The Dark Alchemist
Code Geass : Nightmare of Nunnally
Code Geass : Lelouch of the Rebellion
Sora no Otoshimono
Fairy Tail
Katekyo Hitman Reborn!
Tsubasa Resovoir Chronicles
...I don't have any favs from the list to be honest.Nor do I dislike them o.0 If you can,post a manga recommendation that do not have an Anime adaptation yet :D Thanks in advanced.