One of the folks in a linked in group I belong to has started a site specifically to hook up guest bloggers. Whether you are looking to do guest blogs or looking for a guest blogger, or both.

My Blog Guest is entirely dedicated to guest post opportunities. Very nice community here as well, since the site also has a forum. It's quite a new site, but gaining members rapidly. And happily, it's free.

disclaimer: I have no involvement or financial interest in this site beyond hoping that it is a success that can benefit me, and the folks that have been so helpful to me on this forum.