elfen lied - was a lame ending, and to make note for everyone the ending to manga is just as bad as the anime if u want to know just pm me,
fate/stay night - was kinda lame but at the same time there is another visual novel after the show called fate/hollow ataraxiawhich goes off a different ending in the first visual novel, where Saber stays.
Samurai Champloo - think they should make a new season
Tenjou Tenge - they stopped at the 2 OVAs without finishing the story to force ppl to read the manga to find out the end
Ichigo 100% - had 5 OVAs after it finished and they still didnt hook him up with a girl
Kono Minikuku mo Utsukushii Sekai - the ending was just bad
Air - killed her off, didnt like it
Ai Yori Aoshi Enishi - Never really ended it that well, wondering if they are gonna make a 3rd season
all i can think of atm and yes i watch 2 much anime <.<
EDIT: On fate/stay, not sure if ppl know this but in the visual novel there was 3 endings if i can remember right one was the anime ending, 2nd was like i said she stays and 3rd cant remember, there is also a high demand for another fate anime so u might see them release it soon. and ya this might shock u but archers identity is Shirō Emiya, the main charc of the anime