If you're 18 or older you can try using something like Amazon's Mechanical Turk system. You basically get paid a few cents up to a dollar per task for doing things like answering surveys for academic studies or organizing data and pictures...stuff like that. If you plan and pick your tasks properly you can actually meet minimum wage and after earning some qualifications you might even be able to exceed it. You have to link a bank account if you want to use it for anything but credit on Amazon though. But as a student, I use it regularly because I'm too busy for a job, but being able to pull in a couple dollars in between classes is pretty nice.
You could do walkthroughs or Let's Plays, you'd be competing with a lot of really big names. If you're going to go that way, try to do it with niche games that have small, loyal fanbases.
There are some MMO's that allow you to monetize services, like how some MMOs let third parties sell in-game items for real world money, like how EVE Online will let third parties sell game time codes and some MMOs let players have out of game markets for real money. Just be very, very careful that what you're doing is allowed, because some people have accidentally crossed the line or made incorrect assumptions about what would be acceptable under the license terms and been shut down and even hit with legal charges. However, that means providing a service which could very well turn into a full time job...and if that's what you're willing to do for money, you should probably just get a full-time job for your trouble.
Or you could grind hats in TF2 :3 No, seriously. Trading hats and selling the hats you get in-game is actually a profitable venture for some people. It will require learning a bit about how to invest and how markets work, but hey, that's how people get rich.