To quote the homepage:
Forbidden LEGO introduces you to the type of free-style building that LEGO’s master builders do for fun in the back room. Using LEGO bricks in combination with common household materials (from rubber bands and glue to plastic spoons and ping-pong balls) along with some very unorthodox building techniques, you’ll learn to create working models that LEGO would never endorse. Try your hand at a toy gun that shoots LEGO plates, a candy catapult, a high voltage LEGO vehicle, a continuous-fire ping-pong ball launcher, and other useless but incredibly fun inventions.Forbidden LEGO, Build the Models Your Parents Warned You Against by Ulrik Pilegaard and Mike Dooley.
Allready on my whishlist.