iTunes Catalog is an application that will let you manage your iTunes library. You can get album art for tracks, and have them added to iTunes. You can also search for lyrics, or purchase tracks from various stores.
The main feature that is really interesting is the ability to publish your library to the web. iTunes Catalog generates some php that will generate a representation of your library. iTunes Catalog supports publishing though Mac OS X's built-in web server, or an external host. Here is my published catalog.
I didn't try it myself, but I think that if you host the published site on your mac, you might be able to play your whole library from anywhere you have network access to your computer.
[via The Apple Blog]