cssmin
This is a Python port of the YUI CSS Compressor. Install it:
$ easy_install cssmin # OR
$ pip install cssmin
Use it from the command-line:
$ cssmin --help
$ cat file1.css file2.css file3.css | cssmin > output.min.css
$ cssmin --wrap 1000 < input.css > output.css
Or use it from Python:
>>> import cssmin
>>> output = cssmin.cssmin(open('input.css').read())
>>> print output