There's pine litter, which you can get in both pellet form (but not every cat likes it, although mine does) and in clumping format. Brands would be Feline Pine, Feline Fresh, Exquisicat, etc. There's also recycled newspaper pellets, like Yesterday's News (which also comes in a softer texture pellet that some cats might take to easier than the harder pine pellets).
Then there's clumping wheat litter like Swheat Scoop, and clumping corn litter like World's Best Cat litter. I've also heard of corn cob litter (by One Earth). Here's an article on cat litter with links to many of the brands I mentioned: http://www.greenlivingonline.com/Hom...ty-litter-bad/
What I do is mix half pine pellets with half Yesterday's News. My cat loves this combo so much that he'll even come in from outside (where he has access to a gynormous dirt vegetable garden), to use the litter box. But then he's kinda weird.