Giant Marble Run
For the 2008 Trunk-or-Treat I built an 8-feet tall marble run. Only it used pool balls instead of marbles.
Sadly, the marble run didn't survive my engagement, marriage, and subsequent two moves. This is the best picture I have. The balls started on the wavy slide at the top, dropping into a weighted swing-arm at the top right. The swing-arm rotated counter-clockwise about 90 degrees, depositing the ball onto the first of two ramps. Hidden behind my backpack is a piece of dryer duct that redirects onto the second ramp. The second ramp also has a spinner activated when the ball passes. At the end of the second ramp, another piece of dryer duct redirects the ball onto a "staircase" -- a series of plastic tubs, each with a hole in one end. When the ball falls through the hole in one tub, it lands in another tub. The last tub deposits the ball in a wavy (side-to-side) track (not shown), after which the balls end up in a cool-whip tub for easy retrieval.
Update: My friend-and-fellow-engineer Eric took a couple of pics: