Someone's making a killing here off plastic cups with holes in the bottom no less, but my son has gotten pretty good for a five year old.
I've gotten over $200 in cash back from them at places I would have shopped anyway! Ebay, Staples, more! I put it at the top because they ROCK. Basically, you get a kickback from Ebates when buy.com or whoever pays them. Win-win. If you like throwing money away, don't use them!