In addition to their amazing 10,000 Year Clock, the Long Now Foundation also has this most extraordinary orrery. 
From the site:
The Orrery is an eight-foot tall planetary display. It shows the relative position of the six human-eye visible planets (Mercury through Saturn). The lower six layers are a mechanical-binary calculation engine, each with a geneva output to a gear that rotates a corresponding planet… The Orrery is primarily made of monel (a nickel-copper alloy) and stainless steel. The planet spheres are ground from natural stones that resemble each planet they represent: the Sun is yellow Mexican calcite; Mercury is composed of meteorite; Venus is orange calcite; Earth is Chilean lapis; Mars is Jasper; Jupiter is banded sandstone; and Saturn is banded onyx.
That’s a beautiful piece of clockwork machinery.
For more information, check out their working prototype, or just browse the photos below:
There is also a rather nice video demonstrating both the orrery and the prototype of the 10,000 year clock: