I’m experimenting using Google’s AdSense service. They give you code to place on your site and it generates context-sensitive text ads automatically. When people click through to the ad’s website, you earn varying amounts of money.
I have the option of filtering out sites it selects that I don’t like. I’ve discovered that it’s reading the text of the weblog, since one set of ads I’ve noticed is related to what I posted here. Which ain’t bad, but I’m trying to fine tune it. (BTW, I’ve edited this post to remove references to the ads that I’ve removed, since Google sees that text and generates ads for it.)