Simplify Media, the mother of all iTunes plugins, lets you share your iTunes collection over the net, and now works with iPhones and Linux:
The Simplify Media Mobile alpha enables you to access your entire music collection on your iPhone or iPod Touch wherever you have WiFi. You can also listen to the libraries of friends you are connected to. Because Simplify Media is the only remote music option that doesn't use Safari, you can browse the web while listening to music in the background. You can also listen to entire playlists without having to go back and re-select each song.
