Mostly, I write about what I can get paid for. I write articles for a website called Demand Studios who contracts with writers and editors to supply articles for several different websites. The one I tend to have the most articles published for right now is eHow. How it works: there is a list of titles to choose from. Some are things I'd never write about (Kawasaki Engine Troubleshooting, for example, or Homemade Recumbent Bicycles). Others are titles I either know about (printing brochures or writing resumes) or can do research about (sciatic nerve pain, or paper vs. plastic recycling). They pay me per article as long as the articles meet their editorial requirements.
I also write for sites that pay you by how many people read your articles. The two I'm working on right now are Associated Content and Suite 101.
And, I want to start making blogs on various topics and see if I can make money on advertising. So far, I just have one and I just started it. I don't even have a domain name yet. It's about creation science and you can see it here.