I had a request for a chocolate peanut butter cake - what kind of cake is that? Is it a peanut butter cake w/chocolate icing, vice versa, or is it chocolate w/peanut butter in it? I've never actually had one, so I'm not sure what it is...

It could be either of the two. There are multiple recipes out there for each combination. It would probably be easier on you to ask your client which combo he or she prefers.

Mine on my site is chocolate cake, peanut butter buttercream, chocolate ganache.