I think it was the only ending of any anime that I was completely satisfied with, I've never cried during one but while the ending was playing I shed a tear.
Kids on the Slope
Penguindrum
Yu Yu Hakusho (just finished a couple days ago, I feel so empty).
Clannad
Angel Beats
No. 6
School Days :snick:
Ouran
Oreimo (f*ck the haters)
Ga Rei Zero
Another
For me, it's been said to death but Code Geass. It's just the result of fully and well developed characters all jammed into a huge and massive climax. Death Note is sort of close, but really far from the same amount of power, as Light was nearly the only character alive at that point that felt fully developed. I have to see AnoHana though, alot of people saying it's amazing.