I've tried a couple of JavaScript packers, but found quite a few of them actually caused the JS to fail (making them quite useless!), however Rick Strahl have made a nice little "Click Once" application which does the trick (e.g. compressed a 15K .js file used on my site down to 9.7K, according to Fiddler).
So for a quick and easy load time performance for your website, remember to pack your .js files - try out the utility right here! (Source Code is also available if you'll like to modify anything!)