Via TechCrunch, this looks interesting: Streampad. From the description on TechCrunch:

...a Web-based media player that gives users access to their digital music library from any computer. Similar to Songbird, it streams your personal library from the Internet but it runs completely inside any browser.

Streampad is a free service. Users download a Java desktop application that stores the metadata from all MP3 and AC3 files (protected and unprotected) it finds on your computer, including those that come from iTunes. Then, when that same user logs into Streampad from another computer, they can listen to music streamed directly from their home computer.