Of all the ways in which I've tried to make online money on the side, this has so far been the most successful. The money I make is applied directly towards my student loans, so if you're looking for money in your pocket, this is not for you. But if you need some extra money towards paying off your student loans, I highly recommend Gradible!
It's basically contract work--writing blog posts, doing Craigslist postings, plus some other random tasks. There's also Facebook sharing options and shopping credit options that I haven't used as much. If you're good at writing, you can make a satisfactory little sum of money. And if you're really good at writing (like I am), then the people who run Gradible will sometimes come to you and ask if you can help out with certain tasks.
The downside is that the work and the availability of tasks can be quite variable. Sometimes there's a lot available to do, and sometimes there's nothing. But, as I said before, it's been the most reliable method I've found so far for making money on the side. After steadily doing tasks all year, I looked back and found, a little to my surprise, that I've paid off an extra $2,200 on my loans, thanks to Gradible.
This is a wonderful site, but it isn't magic. You obviously have to do the work, and you'd better be good at writing. Depending on the task and on how easy the subject matter is, I can normally average from $8-15/hr. It's up to you to determine if this is a reasonable rate for your time. For me, right now, it is.