I felt the best final fantasy ending was FFX. FFVI through to FFVIII were better games but the excellent voice acting and advancements in CG technology utilized in FFX immersed me so much, it was like watching the end of a really good film.
On the Final Fantasy front, i really hated FFXII storyline and characters, never bothered completing it due to a complete lack of affection for any characters there. The gameplay was fantastic though.
Other endings that have stayed in my memory are Metal Gear Solid, Half Life 2 (who doesn't love the Gman), Call of Duty 4 and Knights of the Old Republic (not the actual ending sequence for that one, but the whole buildup to the end in general).