Challenge your friends in Crack Attack
As you can gather from the title, Crack Attack is not a Flash game. It's a time waster that you have to download; we don't see too many of those around here. Having to download a game is a pretty hefty barrier to entrance, so a downloadable game has to be really good for me to cover it.
This one is. In fact, my girlfriend (a leading authority on Crack Attack) goes so far as to describe it as "engaging and breathtaking." Your goal is simply to join three blocks of the same color and make them vanish. This sounds like the same old same old, but Crack Attack manages to make the process really interesting.
Granted, the single-player mode is not that much cooler than your simple Tetris or Bejewelled. You need to keep the screen clean while the blocks keep rising, and the blocks that you clear keep turning into "garbage."