I actually dont trust websites that claim to pay you money or a free iphone or anything. Its just to good to be true. Just be careful on that site so you dont get swindled.
There are quite a few reputable sites.
http://prizerebel.com for instance.
From that site I've won:
Xbox 360 Wireless Headset
Metal Gear Solid 4
Mega64 Version 1 DVD
and a PSP charger.
You just fill out surveys.
Another one of my favorites is
http://moola.comYou start with a penny, and you play games. When you win, you double your earnings. When you lose, you lose it all. It can be frustrating at some times, but its worth it when you see the check. (Highest payout was $100) It's also linked to sites like Newegg.com and Bestbuy. So when you buy stuff from them, you get a % of that money back in Moola.