I've just managed to hear some of the Halo 2 soundtrack that's being released in November.

Halo 2 Soundtrack Vol. 1 cover

Anyway Incubus have a few tracks on there (4 if my memory serves me), I've put together this little snippet (360KB/WMA9.1) of the first one - Follow (1st Movement of the Odyssey). Just thought them doing the Halo monk voices was kinda cool.

It just really sucks that they're going to release a second album, no doubt with more of the actual stuff in the game, after all that's what soundtracks are for right? However the first album does have Earth City which is an absolutely kick ass track.