Putting the obvious great anime endings aside, like Death Note, Samurai 7, Code Geass, Baccano, Durarara!
*Keep in mind I haven't seen nearly enough animes yet...I haven't even seen Neon Genesis Evangelion yet*
My favorite ending is probably Ouran Highschool Host Club, but since it is like my favorite anime, maybe I won't count it...instead i'll say....Toradora!
I have a really big soft spot for Toradora!
For a slice of life/romance anime it was pretty darned good. Things played out in ways that would happen very much in real life and I couldn't have asked for a better ending to the series.
Taiga and Ryuji are probably one of my favorite anime couples. *Behind Haruhi Fujioka and Tamaki of course!*
**I also really liked Gun X Sword, the show was great the way it played out, it had a really interesting cast and action scenes and there was a scene near the end that I quite liked alot.