I did some research to make sure I was getting the most out of my rebate sites and found this site that seems to outdo most others in the % cash back department.
Kohl's = 6.5%
Groupon = 15.5% first purchase. 5% after.
Restaurant.com = 31%
BJ's = 3%
The Groupon cash back is HUGE for me. For example, I bought a Memory Foam bed topper for my daughters old full mattress for $119. With the 15.5% cash back, it was actually $100.
Use this link to join!