As you all know, we at WFAC and StartingStrength love the trebuchet. Aside from being intrinsically cool, it is a good way to illustrate concepts of moment and acceleration that apply to lifting weights (see p204 of Starting Strength 3rd edition).
Oakland Ballisticsunderstands these principles and also sells a nifty little mini-trebuchet kit.
Video will be forthcoming.
You can get your very own from the Oakland Ballistics website or indirectly through Amazon.