I started with Ebates.com and then found mrrebates.com. Very similar, but I've found myself using mrrebates about 4 to 1 lately. Its % off is always either equal to or higher than ebates, com. Also, there is a "referral bonus" of $7.50 PLUS (and I just found this out myself)... when a referral of yours makes a purchase... you get 20% (!) of their rebate. Mrrebates.com holds your $ for up to 90 days (returned merch, etc), but "your account" page gives complete, data about all your funds and activity. And, the site sends periodic reminders about what money IS available, encouraging you to have it sent. Whatever $ is due you is just a click away.
If you are a rebate shopper, you will love this site.