environmentally friendly kitty litter?

Right now I am using cheap clumping litter but I am thinking of finding a more environmentally friendly alternative, if possible.

Any suggestions?

I would prefer not to spend a fortune on this, but a small increase in cost is alright.
I also prefer clumping, but I could also get used to non-clumping if I had to. Main disadvantage would be that I don't have a car... so taking the non-clumping kitty litter home could be a challenge.

You may have some luck with this thread.

http://thecatsite.com/forums/showthread.php?t=146438

I've been using an Australian litter called Catlux soft wood clumping litter which is flushable. It does track but its the best I've used, no smell & a 6 litre bag lasts up to 2 weeks with one cat. Can be used as garden mulch & soft on kitties paws.