When We Were Very Young - AA Milne poems
The Tiger Who Came To Tea - Judith Kerr
Anything by Eric Carle (Hugry Caterpillar, Mixed-up Chameleon, Busy Spider...)

Those are joint favourites. DS's favourites are anything with trains or cars in - Thomas, Roary and Bob the Builder especially. *Sigh.*

We do like all books and have loads of them, but other than the ones mentioned above, they go through phases of being read and being on the shelf.