We do like to make stuff. One of the Christmas presents this year was a fabulous model trebuchet. A what? Watch Lord of the Rings (third film, Minas Tirith battle) and you'll know. Basically, a war machine for hurling heavy stuff at the enemy - it uses a counterweight, so there's no need for gigantic rubber bands (which can be hard to come by in a war zone). Just another example of physics helping us.
This one is only big enough to fling a pebble. It's very satisfying.
I met the gent who makes these kits at a local market. He sells them on ebay too though, so have a look here if you think you can afford less than $20 worth of fun.