I was just flipping through the channels and saw G4's Halo 3 Countdown Launch which offered live coverage of the product launch in New York city. Master chief just handed the first copy to someone who'd been standing in line for a very long time - so it looks like Halo 3 has officially launched.
The composer of the music for Halo 3 is Marty O'Donnell. I found some interesting videos containing interviews where he discusses his work on the project. I've embed them below. You can also see them at http://www.gamevideos.com/video/id/11005. Click the "MENU" on the player to see related videos.
I'll pick up my copy of the game in the morning, so if any readers want to get together, email me and we can swap gametags.