I'd have to second (or third) the Scaredy Squirrel. Just bought that one for my daughter and I don't know who cracked up more, me or her!
My other funny faves are:
Knuffle Bunny
Good Boy, Fergus!
Dog (by Van Fleet)--though, maybe this is more appropriately categorized as a board book
The Monster at the End of this Book
Diary of a Worm