my cousin does these as a living lol.
buys a $50 gift card, american express, signs up to those offers, has a sheet of personal details he got off another site and signs those names up. gets loads of stuff.
Prize Rebel works great (PM me for my referral link
), these sites take awhile, and usually are hit and miss, but hey its free stuff. I have gotten about $50 from them. Best thing is how you can order from pretty much any site on the internet, from Steam to Dealextreme to Ebay Buy-It-Now.