I buy a lot from Barbi at Pet Products By Nature, so Crash has gotten used to a heck of a variety of wood in a rather short lifetime (he's just about 3). His favorites are ocotillo, white willow (the chunkier the bark the better), pecan, and pumice.
I also collect willow and grape vine wood that grows organically in our yard and clean/bake it for him, besides ordering balls and wreaths from ForCHINate chins.
And then there's the rare but *adored* disposable bamboo chopstick. They're a rare treat because they're by far the messiest thing he has *ever* had access to, and there is a slight splinter risk, so I watch him carefully while he shreds the thing. They're a great distraction while weighing or if he's in the car.