I've been using SyntaxHighlighter to highlight code portions on my site for a while. Ok, I haven't posted in seven months, but when I was posting more often, I did all of the code formatting by hand, and the capabilities were about 90% of what I wanted them to be. There were a few brushes that didn't quite work right -- (The perl brush, for instance, replaced all of the >'s with >. Thankfully, one of the user community stepped up and fixed it.) -- but, on the whole, it really did a nice job. Posting said code, however, was a bit of a formatting pain and I was looking for a more convenient way to do so.
If you happen to post a lot with a particular language, feel free to change the defaultValue to something more relevant. I chose sh because it's short. You could, alternatively, choose nothing.