3M Colorquartz has been suggested as it comes in many colors and is cheaper than the Tahitian Moon Sand that's sold in pet stores. You can also use playground sand - very inexpensive for a large amount.
I just have one question of my own... where can you buy the 3 M colorquartz sand?
I use play sand for reference...3 pound for a huge bag and after a good rinse it went straight in and has no bother...i have a few fish in there doing a good house cleaning for me everyday and keep the sand churning over.