I recently came across a gaming site mentioned by Nick Gonzalez at Techcrunch called Kongregate. Kongregate is a website that hosts user made flash games with a community built around the games. Think of youtube or xbox live type community where if you register, you can chat with other players during a game, you can earn points with special achievment bonuses each time you go further up the ranks of players. You can still play the games without registering, but you can't really maintain your "levels" and you can't chat without doing so.
My favorite games that I tried were:
Fancy Pants Adventures - sort of a pitfall type of game - above is a screenshot of this game, but the screenshot doesn't do it justice. It's simple, but it is fun.
Warbears - another fun one. This one is more of a visual role-playing game with puzzles to solve
Bowmaster Prelude - Shoot bows at enemies to protect your kingdom. More of an action game
Pinboliada - Hard to describe - you use the mouse to shoot pinballs....
I think Kongregate is a great idea and has potential. Give it a shot for some free games as well as a nice gaming community.