Bare Bones Software : PRODUCTS : TEXTWRANGLER : Download
Text Wrangler is a "lightweight" version of BBEdit. It was a commercial product, version 2 is free. The free version is a very powerful text editor. I use a similar product for Windows that retails for about $70.
BBEdit is a programmer's tool, but most of us will find value in Text Wrangler. I've been using BBEdit Lite for a while and will now move to Text Wranger.