For Tetris I like Tiltris. It uses the accelerometer. Why RIM included a demo of a non-touch Tetris game is beyond me. You can get Tiltris from getjar.com
Also, for multi-player I said before GT Warship on App world is a dream. I know I said battleship. But that's basically the game. Anyway it is not out yet for the 9550. Or at least it does not come up when I search on my phone.
When that comes out snap it up... I have been searching for it every day!