Personally I've hacked an old DVD case by taking out (most of) the DVD ring, cutting the ends off the booklet-hooks and shoving a couple of small shims in the bottom. I haven't put in a hole for a headphone cable yet (I use a separate MP3 player) but that wouldn't be hard as I've specifically left a gap in the shims around the headphone and USB sockets for this purpose. Not only does it leave you with a pretty good level of protection, it also means there's somewhere obvious to store it -- in the DVD rack!