does anyone have any good uses for sawdust?

i've used it for:
* mulching out weeds in the backyard
* given it away for rabbit cages
* made firestarters (melt wax, mix w. sawdust in egg cartons, use one to start fire, works really really well)

anything it shouldn't be used for?
*Walnut is BAD for horses, and will kill flowers/bushes if used for mulch

I don't like throwing stuff away, and like everyone here, i'm sure, i make tons of this stuff. ok, maybe not tons. but a lot.