Ebates is one of those sites that works well if you buy a lot of things online. I mean, if you are going to buy something anyway - simply go to ebates.com, click on the online store that you are planning on purchasing from, and you'll accrue additional discounts. 

At the end of each cycle, they send out "Big Fat Checks" with the amount that you accrued.  It's not a ton - but it's always fun to get a little discoutn here & there.