iDJ
accessTunes streams your iTunes over the web for all to hear. $15 shareware, no word on whether Apple will try to stop it or not. Requires OS X.3+ as well as punching holes in your firewall. Lifehacker has some
commentary on it. See, now this sounds like a sensible shared music solution for music lovers. What are music collectors if they can't share what they've collected?
Let's see, iTunes over the web, portable wireless web, why would you need to carry around a hard drive? Maybe Apple won't approve after all.