That expensive smartphone in your pocket might actually earn you some pocket money. Although I wouldn't go out of my way to perform any of assignments, if you happen to be in the neighborhood or store where one of these apps pay mobile workers, why not earn a few bucks on the side? Some apps also pay you to take surveys, perform searches in your mobile browser (as usual), test new apps, or other easy things you can do in your spare time--while waiting in the checkout line, for example.
There are tons of these apps available, but to earn the most rewards, it's best to concentrate your efforts on one or two of them, so you build your credibility and rewards potential. Here's my list of the 7 most popular apps that pay you to do what you're already doing.