I really liked the endings of Welcome to the NHK and Itazura na Kiss, although I suppose I liked them largely because I already liked the bands involved even before seeing the endings. Go!Go!7188 is one of my favorite bands and Kenji Otsuki, whose songs also appear in the opening of Sayonara Zetsubou Sensei, is a great musician.
I also have a certain fondness for the ridiculousness of the ending of Excel Saga. It's not necessarily a great song, but I feel compelled to include it anyway. Normally I skip opening and endings after seeing them once or twice, but I think Excel Saga is the only series I watched the ending credits of every episode. After 26 episodes I still found it funny. The last episode has a slightly different ending and it's even stranger.
@sharingan_eyes:@SSJjanemba: Those two are faves of mine as well.
Trying to stick with theme songs or at least songs that were sung by the voice actors or super related to the series lyrically...these are cheesy and kinda sound like elevator music, but they're like the only ones that I listen to for every episode