One of my favorite Apps for PC/Mac/Linux and iPhone/iPod Touch is Simplify Media. If you don't know Simplify Media is an awesome program allowing you to stream your iTunes Library over the internet to your other devices / friends computer. I've been using their service for a long time now and couldn't be more pleased accessing my music library from anywhere I can pick up some wifi.
For a short time (first 100,000 downloads) Simplify Media is a
FREE download through the appstore. Pair this along with their free desktop software and you gain access to all of your music while on the go.
Simplify Media works with your iPhone over edge, wifi, and 3g.
Grab it from the app store while you can!
If you don't have Simplify Media on your computers already head over to
their site for a free download.