Where can I find free games to play and download onto my computer?

Are there any sites that have popular computer games like Diner Dash that you can download for free?

See, I hate playing games where you can only have it for an hour because then I want to finish it but I really don't want to waste money. I've been using MostFun.com but the games on there seem really old and there is nothing new. Does anyone have any suggestions?