You can go through Ebates before doing any online shopping. If your store participates (over 1,000 stores do), you'll get between 1-6% cash back on your purchase total just for linking to the store through Ebates. They send you a "Big Fat Check" every three months provided your earnings are over $5.01. If not, they just roll your earnings over to the next quarter. I just got my first "Big Fat Check" in the mail. I mean, it was only for $15.95, but still. As a bonus, right now you can get a $5 credit just for signing up with Ebates. So, go check it out!
Install the Swagbucks toolbar on your computer and then use Swagbucks as your search engine. You'll earn Swagbucks for every few searches you do. Once you get enough, you can trade them in for gift cards, prizes, or cash. 450 Swagbucks gets you a $5 Amazon.com gift card; 700 Swagbucks gets you $5 in your PayPal account. I've been using this for a couple of years now; I usually redeem my Swagbucks for gift cards right around Christmas time.