How do I optimize my stylesheet by removing unmatched and/or unnecessary CSS selectors

I have inherited a massive stylesheet with many thousand selectors and I'm certain that a good number of them are unnecessary and never actually match elements on the site. In the interests of optimizing, I'd like to remove those orphaned selectors/rules.

Are there any tools that would allow me to compare the CSS against the entirety of the site to identify which selectors are required and which are not?

The site has AJAX components, so writing a curl/wget script to traverse the site and then loop through each selector and grep for a match isn't particularly feasible either (even though that would be kinda fun...)

All suggestions welcomed.

Thanks, JD