Midir & Etain have been using Feline Pine for a few years now. We love it. Not dust, no awful cat urine smell, its flushable, and you can even dump it in the garden if you want (I hear this is good for repelling deer and rabbits, but since I live in an apartment, I haven't tested it).
It's inexspensive and readily available at most stores including wal-mart, target and petsmart.
I like the fact that they aren't getting all kinds of funky chemicals on their paws or inhaling that nasty dust found in so many of the clay and clumping litters.
Since discovering Feline Pine I haven't bought anything else, but before that we did try some of the crystal litters (that was back when they first came out) and wow, is it painful to step on that stuff when they track it out of the box onto a nice hard floor