In this recent post to his blog Linesh Jose shows you how to create a simple PHP-based compressor for your CSS (using some string replacement methods and a regex or two).

CSS or Cascading Style Sheets is a language used to describe the presentation of a document written in a markup language. If you're developing a very complex design for your site, CSS scripts become very long, and takes too much time to load. But a compressed CSS script can help your website load faster and easily maintain its functionality. Here, I've created a very simple CSS compressor using PHP to compress or reduce CSS script size.

You can read through the example code and see how it all works or you can download the code and see a live demo of it in action. His script does the compression on the fly, but it's not a far stretch to get it set up as a part of a build to output to a file on deployment.