Digital Orrery [dynamicdiagrams.com] by Piotr Kaczmarek is as simple as beautiful: it shows our solar system according to the Copernican (sun-centered) or Tychonian (earth-centered) model.
Users can rotate the whole solar system by dragging the outer ring or allow it to move automatically by adjusting a slider in the top left. Specific calendar dates can be set, individual planets can be traced and speeds can be changed. Now, if you, just like me, did not know what the term orrery actually meant, you have learnt something.
. Grant Tour of our Universe
. Solar System Music Box
. Solar System Scale Model
. Powers of 10 (and the Simpsons version)
. Relative Planet Size Movie