There are 2 I use, one more frequently than the other:
Points2Shop is the first site I started using, and is the one I know use the least of the 2, simply because the other appeals to me more. Points2Shop makes you do offers (which could be surveys or other things) to earn points, which can then be used to purchase rewards, all of which are ordered from amazon.
Long story short, it works! I got an EasyCap capture card and HDMI cable from it, both came quickly and were as good as new (you could buy new stuff, but it costs more).
If you want to join, use this link please: Points2Shop
This is the site I now use more, simpy because I find it more fun and appealing. However, signing up for both sure isn't a bad idea, 2 sites = more rewards right? Swapit is the newer of the two sites, and works in much the same way as Points2Shop. However the surveys on Swapit seem shorter, and the games you can play seem more fun. The only drawback is that all the stuff is being bidded on, so you could get outbid (think ebay, only free).
This site also works, my friends have got a lot off it over the time they've used it and I'm trying to build up some swapits to get a game :)
If you want to sign up, I would appreciate it if you used this link: Swapit
Use this code if you want to sign up at a later date: r8ktk3