(This isn't sponsored. I honestly use and love these sites!)
Srsly, ya'll, you should check out Swagbucks. Since joining in November I've gotten $100 in restaurant.com gift certificates and $45 in Amazon gift cards. Mostly free! (I did join the Columbia House DVD Club, but I'd wanted to do that anyway.)
The easiest way to get Swagbucks free is to use their search engine toolbar, and to refer other people. They've got all sorts of stuff--if I were patient enough, I could get a Nintendo Wii for free. I'm just not that patient!
Also, MySurvey.com has gotten me lots of free products and several free hardback copies of my favorite authors' new releases (via Barnes & Noble giftcards). They recently re-did their rewards system, too; I just cashed in 1100 points (totally free) for $10 on Amazon.
I'm hoarding Amazon gift cards from both sources; when I have enough, I'm buying myself a new iPod! C'mon, help me out with it.
Also, if you have a blog and would like to try sponsored posts, I recommend Blogsvertise and Social Spark (I made $80 last month there).