You could also go with any one of the many other Dr. Seuss books, and still have a cute party. Just look at this Horton Hears a Who display on Kara's Party Ideas.
Here is one of Dr. Seuss ' classic books- One fish, two fish, red fish, blue fish. I have pulled together some snack ideas, fun activities and art.
A Dr Seuss theme party is not just limited to children's birthday Dr Seuss Cat in the Hat Invitation One Fish, Two Fish Birthday Invitation.