Momentum Missile Mayhem is one of the more addictive games I’ve come across in a while. You can even download it to play offline, which helps the performance somewhat.
The game Triangles makes my head hurt. Try it! ;-p
Check out MapMSG.com’s game Statetris, a Tetris-like game where U.S. states must be guided (and in higher levels, rotated) into place onto a map. If that’s not challenging enough for you, try Statetris-Europe or Statetris-Africa.