I have made money on Elance, Textbroker, Demand Media, Triond, Web Answers, some personal blogs, (Blogger and Wordpress), Infobarrel, Hub Pages, and Red Gage. I've also made a bit of money on real world publications, nothing huge though.
I know there are lots of other places online to write for money. You could spend 24 hours a day slapping up content on all these various sites, no problem. So people do, too.
I made the most money the first year I worked freelance, but lost interest over time. Five years in I'm not so interested in making money online anymore, I just write for a couple of clients I picked up at Elance and post a Hub or blog entry now and then. The thing is, it gets to be a grind and if you love to write it takes the pleasure out of it if you go at it full force all the time. Blah blah blah yeast infection, blah blah blah product description, blah blah blah hotel review, etc, and so forth.
After five years I make an annual income about equal to a part-time outside retail job. This is because I don't work at it very hard and I'm not very tech-savvy. For me, it's fine because I have lots of other things to do--an acre of property to care for, grandkids, kids, a dog, a cat, a spouse--and there aren't many jobs where I live. Plus, I'm near retirement age, and I've had enough of the rat race.
If you want to make money you can though. It's just lots of work. It doesn't come easy at all.