Under the Hood, by French author-illustrator Christophe Merlin, is one of the great ones; it's also the current favorite of my three-year-old, Griffin. (Naturally, it has a vehicular theme.)
It's not that the story is anything fancy—Mr. Bear, a mechanic, has his car break down, and must organize his rather lazy assistants, a crocodile and a mouse, to fix it. But the execution, which is usually where one finds the action in great genre books, is both clever and very aesthetically pleasing.
Merlin's retro-style art is reminiscent of that of classic 20th-century European illustrators, and the flaps and pulls are designed in a slightly different way than those of the average U.S. flap book—at different angles, and incorporating the art in different, often surprising ways. Even the book's paper stock is a little heavier than usual, a little more textured, providing a touch of sophistication not usually associated with flap books featuring Mr. Bear. It's more than enough to set Under the Hood apart, as Griffin would be the first to tell you. (Though his way of telling you would be to tell you to read it to him at bedtime for the 20th consecutive night.)
[Cover image courtesy of Candlewick Press]