With a book theme, of course the invitations have to look like the book, right? I scanned in my old copy and prettied it up a bit in photoshop (30 years takes its toll on a well-loved children's book).
I erased "A Little Golden Book" from the front cover and replaced it with "A Little Baby Shower" in a similar font.
I just love that I was able to get the back cover and the trademark spine on my invitations, too. (Even if the spine is a worn silver now instead of the original gold. I like the worn look better, so I didn't try to fix it.)
I even put in the inside cover, with the bookplate and everything. So cute! The party information was written in a similar font to the original story and I put in an illustration from the book.