These sites allow you to play games for prizes, some let win cash.
If you have any question, let me know.
Winster.com
You can play for prizes, and you can cash in your points for gift cards. You can use your points to buy all sorts of goodies. No cash on this one that I know of yet though. I am still looking into it. I will let you know. You also win trophies.
My favorite game on there is Slot Social.