daft idea, can't delete the thread
Have you seen Ralph Steiner's film? I highly recommend it and you should probably watch it and learn yourself some things.
I like the elliptical and square gears the most. Got popcorn?
I like the ratcheting ones that turn a steady circular motion into an arm that moves a gear intermittently. Quite the important mech for clocks/watches, and I like my watches.
I love thread abstraction. Especially when it's all linked together with gears.