Drag ‘n’ Drop CSS Compressor – excssive
If you like applications that are simple and get the job done quickly, you'll like excssive.
It is a free-to-use CSS compressor where you can drag 'n' drop any number of files and they will be compressed instantly.
The application merges all files into a single one and enables you to reorder the files (so as the output) again with drag 'n' drops.
In case, you are not compressing the CSS files dynamically, excssive is a must-bookmark for easily minimizing your stylesheets.
P.S. The source of the application is also freely available.