Just a quick one:
Similar if not even more useful to the in my previous post mentioned LINQPad is Paul Stovell’s jQueryPad. Guess what it does 🙂

jQueryPad is a fast JavaScript and HTML editor. Just start it, enter the HTML you want to work with, bash in your jQuery code, and hit F5 to see the results. Say goodbye to ALT+TAB.

jQueryPad