Hmm.... I've got an air powered potato gun... I brought it to school with me last year. One of our dorms is a 12 story tower, and I have some friends who lived on the 8th floor, with a balcony. We launched all sorts of stuff out of this sucker, including filling the barrel (about 3 feet long, 1.4" pvc pipe) with ketchup and launching it up into a ketchupy cloud. I think we hit some cars with that one...
Anyone know how to make that coil-gun debaser was talking about? That sounds interesting...