Just found this today - it’s an online CSS editor. Basically it takes a copy of any page, and then let’s you edit the css in “real-time”. I say real-time in quotes because it actually makes a copy and that’s what you are editing, but it’s very cool. You can “play” with a site and see what tweaks to a CSS file will do live.

Check it out here:
http://www.cssfly.net/

You can also move the CSS editor around to make page viewing easier.