CSS Tweak is a handy tool that'll do the dirty work of slimming down your stylesheets for you. I just found it today, but I think I foresee a pattern for the future:

1. Validate CSS
2. Tweak CSS
3. Profit!*

If CSS Tweak were any easier to use, it'd be... well, I can't even think of an analogy; that's how easy it is to use. Simply browse for your CSS file (or paste the code into a textarea), use the checkboxes to tell it what to tweak and what to ignore (I recommend choosing "Leave my layout alone!" instead of "Remove white space," unless you like seeing all your code on one line), click the "Tweak" button, and voila! CSS Tweak works its magic and prepares a new, slimmed-down file for you. It even tells you what percentage of fat was trimmed. The developer, Andy Peatling, has set up a forum for questions, comments, and general praise-singing.

* Okay, maybe not that last step.