Some of my son's favorite's are the Laura Numeroff books!
If you give a mouse a cookie
If you take a mouse to school
If you give a moose a muffin
If you give a pig a pancake
If you take a mouse to the movies
If you give a pig a party
Those are the ones that he has :) I think we are missing a couple. He loves them.
The Curious George Books are pretty cute too!