I just had a friend forward me a challenge to this new game site, Big Bomb Games. They have three flash games online, a Breakout clone, a BlackJack game and a game I have never seen before, a mix between Marble Madness, Othello and a demolition derby.
They seem to be just starting out, but you can register and post your scores and challenge friends to beat your scores.
Check it out at http://www.bigbombgames.com