"The Great Silence" - a spaghetti western by Sergio Corbucci, has the most shocking and downbeat ending I've seen. From an artistic point of view, that is my personal "best", but, depending on the film's context and quality, I LOVE a nice, happy, plausible resolution as much as the next person!
How about The Blair Witch Project? I love that one! And Edward Scissorhands; when Kim (Winona Ryder) says that it didn't snow before Edward came down, and afterwards it did. So sweet! And Billy Elliot; the look on Billy's dad's face when his son is performing on stage brings a tear to my eye! He looks so proud. And the ending of The Color Purple has me bawling like a baby when the two sisters meet again after so many years apart. I know, I'm sad, aren't I?! Finally The Wicker Man; the image of Edward Woodward burning to death inside it will stay with me for a very long time!
Wasn't keen on the ending of the sixth sense - it was obvious from halfway through what was going on - from the lack of interaction with anyone else with Bruce Willis
I agree with you, Chazza, on The Sixth Sense. I guessed the ending as soon as Haley Joel Thingy-Wotsit whispered to Bruce Willis, "I see dead people", which kind of ruined the ending for me. Although my mum, bless her, didn't figure it out until Brucie's wife dropped the wedding ring! She was a bit slow there! On the whole, though, I thought it was a pretty good film.
fight club as mentioned before, the game, se7en (all david fincher films incidentally) 6th sense & unbreakable too. memento was good as was usual suspects.
The Others had a good twist in the end, like The Sixth Sense, it turned out the main characters were dead throughout the film when they thought they were actually alive.