CSS out of control

Are there any utilities that will crawl a site and determine which css rules are in use and which are not? We have a large site and a huge CSS file (--don't blame me I just got here). And, I think much of it is not being used however I'm afraid to strip stuff out just in case.

The file is confusing and difficult to manage and I think if we can trim it down by getting rid of the unused rules we will have a good starting point to go through and try to make it better.