Lol, me too, that ending totally blew my mind for some reason.
My favourite twist would have to be Saw, my eyebrows hit the roof watching that for the first time, and it was a pleasure to re-watch it with my Dad and see his reaction.
There's also the twist at the end of Se7en which is good, despite someone having already spoilt the ending for me a few years prior to me seeing it. Somehow i managed to remember what they said happened though unfortunately.
And who can forget the twist of the 80's in Star Wars: The Empire Strikes Back!