If you download Simplify Media onto an ipod touch and your PC or Mac, you can access your complete itunes library on any wireless network onto your ipod. Its just under 3 quid from the itunes application menu.
More than that you can also access friends libraries (by invitation).
The security of this worries me, but I can't find warning of dangers at present.

I have to say, that accessing my complete library is astonishing, especially as most of mine is lossless, and quality is excellent. It will work on winamp and others. The big breakthrough will be when you can access Spotify through it (its being worked on they say)