I have been a member of Ebates for well over a year.  It is absolutely free and they pay you cash when you make purchases though there website.  As you may or may not know, website often get paid for referring you to another site where you make a purchase.  Since Ebates is doing the referral they get a percentage of your purchase.  The nice thing about it is that they share that percentage with you.  Percentages vary by store, sometimes even daily.  If you ever plan on making a purchase online signing up is essential.  There is no sense in not getting money back when it is this easy to do.  Sign Up Here. Another similar site is Mr. Rebates.  Click Here to sign up for Mr. Rebates as well.  I suggest you sign up for both because the percentages for stores vary from site to site.  For example, one day Kohl's might be 4% on Mr. Rebates and only 3% on Ebates, and the next day be the complete opposite.  

Here is the Official About Ebates Blurb from their website:

About Ebates

Ebates is the pioneer and leader of online Cash Back Shopping. The company was founded in 1998 by two Deputy District Attorneys in Silicon Valley who used to prosecute online fraud & identity theft before starting Ebates (so you can be sure we are very into secure online transactions!). So go ahead, sign up and start shopping now. Joining Ebates is always free – you'll never pay us anything. And four times a year or more, we'll mail you a Big Fat Check, or transfer the money to your PayPal account if you'd prefer. We can even send the money to your favorite charity. All 100% free. People often ask: "This sounds too good to be true, how are you able to do it?" It really is quite simple. Just like almost every other online shopping center, we get a commission from the stores when you make a purchase. Instead of keeping that money – like almost all other sites do – we share it with you! So, as long as 1200+ of the world's top online stores are happy to pay a bonus to attract the new, valuable customers we send their way, Ebates is going to continue to send Big Fat Checks to our satisfied customers across the globe.