I found ebates somewhat frustrating because of all of the popups and toolbars, so I just use fatwallet to get cash back rebates (it has worked fine for me so far, and they follow up quickly when a transaction doesn't post and I let them know, also it usually pays out within a few weeks, not quarterly). Liz, what rebate site do you use?
I use retailmenot to search for coupon codes for specific stores. Retailmenot has a red/yellow/green indicator on coupon codes that lets you know if they are working for people, and users leave comments that are sometimes helpful. I use different sites when I'm looking for food/drugstore coupons, since that's a whole different thing.
Generally I think these sites are all fairly similar, so it's kind of whatever works for you, unless one has better cash back percentages.
I would use a filter or sign up with junk mail, because they do email you pretty much daily or more often.
ETA: It looks like these sites will compare the rebates from various sites for a particular store: http://www.cashbackmonitor.com/ or http://www.cashreporter.com/ . I might need to venture on from FatWallet as they don't appear to be the highest for some places I shop often hmm....