Ooh, good options! I'd seen some stuff on the Lego tires but they seemed mostly car-ish, and I've only seen some of those WPL ones. The others may be real handy for some projects (rubbing hands together.)
Wrt wheels, for folks with a printer, I did up an OpenSCAD that takes various dimensions from the tire (inside width, lip width, thickness, etc) and spits out a generic wheel with optional lugs and hex drive. It can also do duals. It's not perfect and it's definitely short on cosmetics, like the base form is
But with some customization of the code you can do stuff like
Anyway, if there's interest (like, does anybody else use OpenSCAD?
) I could prolly figure out how to put it up on github or someplace for public use/contribution/fiddling.
-- A