Textmate is a code editor (and a very nice one). Coda is a web design tool, like Dreamweaver (integrated preview pane, built-in GUI support for CSS mangling, etc.). Coda looks to be a lot cleaner than Dreamweaver. I like it -- but I'm not sure I do enough web design to justify switching. It has more to do with the time to learn a new app rather than the cost; while Dreamweaver may be nasty, I've been using it for a long time. If I found myself needing to do a lot of web design, I'd definitely consider a switch. Coda seems elegant and intuitive.