In that case, you may want to take a slightly trial-and-error approach.
You're running a Wordpress site, so that means you have a finite number of template files.
Go through those and pull out all the elements, classes, and IDs that you use in your templates. You could use a text editor to search for "<", "class", and "id" to find your targets.
Then, go through your CSS and look for CSS that isn't in that list. Remove it, run through a handful of pages and make sure you didn't accidentally break anything. (You could try commenting it out with /* */ around the block, then testing, and remove everything at the end).
If you get a steady supply of traffic, I highly recommend doing this on a local/test server, as you'll probably break stuff.
However, looking at your site, it looks like there is only 40kb of CSS (unless you somehow have control over the ones on the fbcdn ). That is a bunch, but unless you think you're going to be able to reduce it by about 50% or more, I honestly wouldn't risk trying to clean it up in one go. Over time you could slowly find bits and pieces that aren't used and pull them out. You can probably find better areas to direct that effort.
Nice site, btw. Very clean.