A while back, I was reading Peppermint Lisa's blog and she wrote about a new kind of kitty litter called Swheat Scoop. It's made of wheat, ground down to the size of regular kitty litter.
The clay kind was nice at first, but the cats kicked up a lot of unhealthy dust, and a lot of plastic bags were used to remove the mess. Also, the clay kind is mined out of the earth, which is not so nice. This new wheat litter comes from a renewable resource, is biodegradable, and can be flushed down the toilet. It also smells better - more natural. You also don't need to put a plastic bag in the garbage every day - just flush it down the toilet.
One word of caution: my cat Lemon thought it was food, because his is sometimes given buckwheat pancake mix. To avoid that, sprinkle the old litter on top for a few days, but be sure to throw that out - don't flush it until it's pure Swheat Scoop.
be efficient: Wash your car on the grass.