Points2shop.com is the best GPT site ive used in years. They hve TONS of free offers that give you cash or points (which you can use for prizes) I found a really accurate review on their site and if you'd like to read it here is the URl.
http://sites.google.com/site/points2shopreviews/
or if you want to go ahead and just sign up click the picture below and it'll take you to signup page
http://sites.google.com/site/points2shopreviews/
or if you want to go ahead and just sign up click the picture below and it'll take you to signup page