Simplify Media have released an application for the iPhone and iPod Touch that will allow you to stream you home iTunes library to you mobile device.
To get started download the Simplify Media Mac client to your home computer and install the iPhone app on your mobile device. Your home computer should show up as a streaming source. You will also be able to connect to up to 30 of your friends who have the software installed.
The Mac client is a free download, while the iPhone App is $3.99.