So I am on my second litter box of wood stove pellets as alternative litter. It absorbs so well, I discovered I have to use less. Umbra's litter box was filled with droppings before even half of the pellets had gotten wet.
The only drawbacks are that Umbra kept snacking on them at first, but I haven't seen her do it since. However, whenever I fill up her litter box she comes running because she thinks I'm getting her food. I don't mean to tease her, but they aren't those kind of pellets. I give her a treat anyway, just so she won't go insane (and plot my murder).
The verdict: thumbs up for wood stove pellets. Inexpensive and super absorptive; what more could you ask for?