You need the non-clumping type. The clumping type retains water, forms clumps, and falls apart. You want the well-draining, non-clumping type.
I use fired, danish clay pellets. I have bought three bags, one of them I put in my plastic soil container (that I use when I'm repotting), to rinse out the dust (which probably wasn't really necessary).
I know this thread is about cat litter but while I was reading it it came up to my mind... What about lava rock? This material won´t clump, it hardly retains any water beyond its porous surface, it won´t fall apart since it is really hard and will provide the adequate aeration to the roots. And if on top of that you add that it is not expensive either, I think it would be a valid candidate to take into account while preparing our soil mixes...
Alain