As an extension to this question here Linking JavaScript Libraries in User Controls I was after some examples of how people are concatenating and minifying JavaScript on the
I'd recommend http://www.RequestReduce.com which minimizes and combines css and javascript as well as sprites css background images and optimizes their PNG compression. It does all of this at run time and caches the output. It requires no code or configuration beyond adding the HttpModule. It serves all cached content with optimized far future headers and ETags to ensure that browsers cache the css/javascript/sprites as long as possible. While it requires no configuration, it is highly configurable and can be setup to run with a CDN and sync cached files accross a web farm.
All javascript, images and css are fetched via HTTP so it can include css and js from third parties and its also a great way to minify/combine .axd resources like WebResource.axd and ScriptResource.axd. It determines the presense of js and css via content-type so the target resource can have any (or no) extension. It runs on any IIS based technology including all versions and view engines of MVC, web forms and "web pages".
You can download from http://www.RequestReduce.com, Nuget or fork from https://github.com/mwrock/RequestReduce.