Our credit card is thru Upromise, so we earn like 5% each month back in cash into the account. Anytime I shop on-line, I just click through Upromise, which is on my toolbar and only takes about 15 seconds to use that step. In doing that step, On-line retailers credit 3-10% per sale and they have never missed one (I keep track so I don't get cheated!). Also, I have registered my cards from Jewel, Dominick's and CVS, but those really only give me back about $3 a year each. I have nearly $1,000 in three years time from all sources. Also, I do E-Rewards surverys through Upromise and earn about $5 a month for those.
You can register friends and family, too, but most of mine already do it for their own kids.