Whenever you make a purchase online, it's a good idea to see what sorts of bonuses or discounts you might be able to get. By first visiting sites like Ebates, Fatwallet, Citi Dividend Mall (for Citi credit card holders) and the various airline merchant networks you can earn some cash back or frequent flyer miles on a surprising number of purchases. Many merchants are featured on all of these sites (such as The Gap) but some are only featured on one or two (such as Tiger Direct) so I find that it's helpful to look around.
When you sign up for Ebates, you'll get $5 cash back credited to your account, which you will receive after earning $5 more in cash back. I've made $60 in cash back from Ebates this year, in part because I was able to earn credit for some larger business purchases. Sometimes you'll find killer deals on Ebates. For example, I used them to try My Wines Direct and got $10 off my purchase plus 7% cash back.
FatWallet also provides a $5 incentive for signing up and works similarly to Ebates. However, I prefer Ebates because they get your cash back to you faster.
The Citi Merchant Network allows you to increase the power of you cash back credit card. I currently have the Citi Dividend card that gives 5% cash back on gas, supermarkets, and drugstores (unfortunately, this card has been discontinued so new applicants cannot get it and I'm sure they won't renew mine when it expires next year). By first going to Citi's website, signing in, and then clicking on a link to the merchant you want to shop with, you can get 5% cash back on all kinds of retail purchases (the offers vary; not all are this high). Airline merchant networks work similarly.
The key to all of these sites is the clickthrough. You must always visit Ebates/Fatwallet/Citi Merchant Network/airline merchant networks first, sign in, then click on their link to the store you want to visit in order to get your cash back. Some programs post your rewards sooner than others--you may see your reward in as quickly as a couple of days or as much as a month. I always worry that my bonus won't come through, but it always has.
I've tried to be thorough with this article, but if I've missed anything or there's anything that's not clear to you, please leave me a comment and I will get back to you asap. I would love to teach you how to get these deals.