A ripe Fraise
I recently found out about a great free text editor through one of my favorite Mac blogs, Minimal Mac. Fraise is a completely free text editor for your Mac. I don't do a lot of programming, but I do open HTML and CSS files a good bit. The syntax highlighting is very convenient.
If you're looking for something a little more robust than TextEdit, check out Fraise. I've been really pleased with it.