I know this is old news, but I recently switched jobs and am doing web development again.  Some co-workers turned me onto the Watir library for Ruby.  Scott Hanselman talks about it here.

I'm not sure I'd call them unit tests, but it certainly makes an easy way to do scripted functional tests.  I've also used it with IRB (interactive ruby) to launch a browser and get to a specific spot in the web app.  When I'm developing something that is in the middle of the app and takes a while to get to, I use this technique and save a ton of time.