Lately, 80% of my YouTube usage has been watching Rube Goldberg machines. Here's a few of my favorite:

The Blue Marble - This entire channel is so well done.

The Cake Server - I love the mechanics as metaphor here. The food theme is infused throughout, and never ceases to delight.

Wintergatan Marble Machine - Not a Rube Goldberg machine per se, but I think it embodies the essence of the concept. As Dave Rupert notes, "It’s raw, creaky, clumsy, and beautiful."