Ive recently started looking into the same thing... I have a job and want to make some money in my spare time.
So far it to be completely honest it looks like the majority of things people talk about in terms of making money online really aren't worth the effort. E.g. all these little reward sites, micro-tasks and such. I mean you can get an extra few dollars for sure. But it takes so long and the pay is compariable to third-world sweatshops. You'll spend hours and hours doing mundane tasks and you'll get sick of it very quickly.
Elance looks like it has potential, but there are so many people you have to compete with who have very strong resumes so it's hard as a new user with no experience. Also as someone just mentioned to me in another thread, everyone just keeps offering lower and lower prices so you end up doing jobs for next to nothing.
There are a few writing sites that seem to offer good rates, but they never seem to have any work avaliable :(
This is unrelated but I have actually made a couple hundred dollars trading bitcoins, but it's not really an ideal thing to be doing. First off you'll probably want a spare $1000+ that you don't mind losing... to put into it if you want to make anything. And the market is very unstable so you have to be incredibly patient and you risk losing money if you mess up.
Ive been using slicethepie.com recently. You listen to music and get paid for writing reviews. The pay is probably better than a lot of these micro-task sites. You get about anywhere from about 6-20 cents per review. You could probably make $5 in an hour if you are good. It gets very repetitive and there's a lot of music that you won't want to listen to. But yeah. $5 an hour is far below minimum wage where i'm from.. Extra money is extra money I suppose, but it's not exactly "job" pay levels.
The ideal thing for me would be to find some sort of site where I could write articles for money, but so far I haven't been able to find anything that actually has work at the moment.
Well that was a bit of a long reply. Hope that helps and i'm interested to see what the other peeps on here say.
Good luck