http://closure-compiler.appspot.com/home

Compress your javascript files using Google’s Closure Compiler.

I tried a quick experiment using Jquery 1.3.2 development edition, using the “advanced” mode of the compiler:

As a comparison, Jquery from jquery.com (here) is compressed to 55.9KB minified and 19KB gzipped.

Google’s Chrome Compiler shaves off one KB or so. Not bad.