A slight remix of PerryT's wonderful Elliptical Gear set. I liked playing around with the gears connected at the off-center pivots, and thought it would look cool to remove the center ring entirely.
You can find the original thing here, along with other types of connecting arms: http://www.thingiverse.com/thing:37659
I've made a new oval gear with a spiral design in the middle. Check it out here: http://www.thingiverse.com/thing:1125461