If you like Bomberman or Tetris...

[Ponyo]

omgpop.com

It's a great place to waste time, and it's fun because you can play against other people online, check it out.

[geno]

I played a bunch on their site last month. I liked the Mario Kart game the best I think, reminds me a lot of the original (though missing some of the flair of the stages).