There are a number ways in which you can set the compiler loose on your code: you can use the open source java command line application, you can simply plug your script into the simple online web application or you can even make use of their full RESTful API.
And just in case you were wondering why you should give them a spin, take note that jQuery have moved to the Closure Compiler to produce their minified scripts.
So what are you waiting for? ;)
Related Link: http://code.google.com/closure/compiler/