I wrote a minor mode for Emacs a while ago that does something similar to what it looks like CSSEdit does. It uses MozRepl to update the current css of a page in Firefox so you can have a live preview as you work on a css file.

I don't really ever work with CSS these days so it doesn't get much use. It's a little flaky as I've only ever had to get it to work for me. But if anyone is interested I could put it up somewhere.