This is the best all-around option I have found: The Plano 3730 box. You can get it from lots of places for about US$7-ish. It holds a lot of discs, but that means different things for different folks. You can fit ten discs per slot unless they're in a case, then you can only fit five. If you want to be able to flip & browse discs, then about eight per slot is the magic number.
In any case, they fit & protect discs really well and are inexpensive.