http://www.creativyst.com/Prod/3/

Free demo page for Creativyst(R) JavaScript Compressor.  Compress JavaScript code and Cascading Style Sheets for faster page loads and better code documentation. We compressed the files in our js folder on this site with this and was able to drop 30.2K off the total size. This is the best one I've found because of the code safeguards that are in place. Some compressors can break the script, but this has worked every time so far.