The first Boynton book that I ordered was Hippos Go Berserk. I couldn't resist a counting book that featured hippos and that had the word "berserk" in the title. Liam likes the book even though he obviously doesn't "get" counting yet. It doesn't quite have the rhythm of the other two Boynton books we own, though. Once he's a toddler, I think he'll really enjoy it.
A few weeks after Liam was born, we discovered a copy of Moo Baa La La La at Goodwill. Liam loves this book. He'll giggle as I read it to him, and it really seems to keep his attention. I recently read that encouraging your baby to repeat consonant-vowel sounds like "ma," "da," and "ba" helps with language development, and I think that reading this book to Liam will be an enjoyable way to do that, as well.
Liam's favorite Boynton book by far is Oh My Oh My Oh Dinosaurs!. He'll giggle and roll onto his side when I read it to him. It's a book of opposites, and I'm pretty sure Liam "gets" opposites about as well as he "gets" counting, but this book really keeps his attention. I'm sure it doesn't hurt that I enjoy the book, too, and he loves the silly faces I make when I read it to him. Sometimes, when he gets crabby, I'll say "Oh my oh my oh dinosaurs," and it instantly brings a smile to his face. I think it's a testament to how much he loves this book.