You Can Count on Monsters by Richard Evan Schwartz. In a work of creative genius (seriously, how do people think like this?) he combines art and prime/composite to form a series of monsters. His webpage gives you the best glimpse of how the monsters work...suffice it to say that prime monsters are frequently eaten by composites. The concept even captivated NPR with a story: Math Isn't So Scary with Help From These Monsters.
Additional resources include:
A poster of 1-100, factored.
A fabulous prime/composite applet. Ask students to compare the applet to the information in the book.
The author has a series of videos explaining more about the book and its concepts.