Well I'm not too sure how well this works, and at the moment it looks like there are only a few people offering stuff to do, but in principle this looks like quite a cool idea.
Pop along to Short Tastk and you can pick small jobs that you can do on line. For some you need to be a US resident, for others you can be global. It may involve adding a link to a blog, following someone on twitter, writing a short article about certain subjects. Take a look and see if there is anything you could do to earn a few extra dollars.