If you're proud of a product, you tend to tell all your friends about it. Rec.fm makes use of that impulse by donating money to your charity of choice every time your friends buy a product you recommend on Twitter or Facebook.
Rec.fm is simple, and not unlike the popular referral programs of other web-based entities. Through their site, you can search for products you like — say, your fancy new wireless mouse — and tweet or post on Facebook about how cool it is (which, let's be honest, you probably did anyway). If your friends take you up on that recommendation and buy the product, a portion of the money they pay for it goes to the charity of your choice. It's a win-win all around.
Of course, you don't want to use this excessively — while donating to charity is great, your friends will start hating you for clogging up their Twitter stream and probably not click on your recommendations out of spite. But if raving about your favourite new toys is something you're prone to do every once in a while, this is a great way to take advantage of that.