He seems to like routine (read "same books over and over and over!) and likes animals, so he really enjoys:
Good Morning, Good Night. (he likes to "tickle" each animal goodnight!)
The Going to Bed Book (new classic!)
So Many Bunnies (subliminally teaches ABCs and rhymes LOL)
That said, MY favorite books are the "I Love My Mommy Because..." book and it's counterpart "I Love My Daddy Because..."). I got it from the library when he was maybe 12mths old (?). They're just GREAT, and you can teach "baby" animal names like cub, chick, etc! We don't own them though :-( I keep saying to myself I need to get online and order them, but just haven't yet!
Oh, and how can I forget....my other favorite is "The Snuggliest Snuggle in the World." It was given to us by a friend for his first birthday! This book is AWESOME and the voices can be really fun to make! He really enjoys it and picks it out first if given a choice of which books to read!