Good games, Dropsy is actually one of my all time favorites as far as the artistic elements of a game are concerned. Beautiful, sad, and silly all at once. Chris Schlarb does an amazing job on the soundtrack, and I really appreciate that there are no words in the game.
VVVVVV is tough as shit at times, play with a controller if you can.
Braid's great, I played the whole thing in one sitting. Fight the urge to look up solutions to any of the puzzles.
I haven't checked to see if they're on sale, but two great puzzle games that don't seem to be that widely known are Snakebird and A Good Snowman is Hard to Build, if you're into that sort of thing. Be warned, Snakebird will take your sanity.