For cash back sites, I used Fatwallet the most, followed by e-bates. Signing up blind for e-bates doesn’t come with any bonuses. Being referred by an existing member gets both the new member and referring member $5 most of the time (after the new member makes a qualifying purchase). Through the middle of February, though, e-bates is currently offering a $10 signup bonus (again, new members have to make a qualifying purchase — by February 14).
So this is a good time to sign up and start using e-bates. To be clear, using the link about does earn credit for me as the referrer, I pass it along only because not using a referral link won’t earn a new member any bonus.