Instructables has this step-by-step guide on how to make your own 3" trebuchet [wiki] from paperclips that can throw little balls of blue-tac to an amazing 4 feet.
You will need:
1 pair of pliers (needle nose would be best but i don't have those at work) 1 pair of scissors (yay for scissors)
7-8 paperclips sellotape thin string blu-tac a piece of corrugated card (approx 6X6") Ballast (I used a bunch of batteries from our recycling box)