[JoachimSchipper]

Google's Closure compiler can apparently do that.

[JonnieCache]

Doesn't work on jquery. To use that functionality of the closure compiler without breaking your code, the source has to be annotated in a special way, or it has to be incredibly simple.

[JoachimSchipper]

I don't know much about this, but do you mean http://code.google.com/p/closure-compiler/source/browse/trun... ? That suggests that it will be available at some point, at least...