Hmmm, I don't think Dat would be a good idea. It's not really random access, and my experience with home decks is that tapes chew up quite easily...

Cd could be good, but it takes alot of space, and is very prone to skipping (Although the buffering would sort most of that..)

I'd go for either slot loaded Hard Discs, or some high capacity minidisk variant (Smaller discs have less vibration problems..) At least until solid state becomes a sensible price.. =)
Jazz