Any recommendations for a CSS minifier?

CSSO is currently best minifier/optimizer.

I like Minify. In PHP and works with CSS or JavaScript.

The YUI Compressor is fantastic. It works on JavaScript and CSS. Check it out.

There's also a .NET port of YUI Compressor which allows you to:-

• intergrate the minification/file combining into Visual Studio post-build events
• intergrate into a TFS Build (including CI)
• if you wish to just use the dll's in your own code (eg. on the fly minification).

UPDATE 2011: And it's now available via NuGet also :)