Apple's event is starting up right now, but in the meantime, they've (inadvertently) revealed iTunes 9 via a page over in iTunes. The new version of Apple's software will include quicker and easier navigation options (you can see the new top menu in the pic above), easy-to-access preview buttons, and new ways to experience media purchased in the store. iTunes LPs will let you have the full album experience with lyrics, liner notes, and band photos and videos, and iTunes Extras will allow you to experience DVD-style extras with movies you buy from the iTunes store.
Expect an announcement at the event in a few minutes -- there is a download link on the page, so we'll also expect to have the software up and running by the end of the day. Sounds exciting!
Update: More info coming out of the keynote right now: Genius mixes are a new way to hear Genius picks, mixed by a virtual DJ. Improved playlist syncing options, and a way to arrange your apps from directly within iTunes.