How can I make a multiple row menu?

I’m an author and as I come out with more books, my menu page has started to wrap. See: http://joederouen.com/.

What I’d like to do is put all of the non-book options (Home, About Joe, Contact, Press, Gallery, Store, Donate) on the top row and the book links centered below that. But I can’t figure out how. Is there perhaps a plugin that would enable me to do such a thing?

Thanks!!