In case you missed it, Halo 3 has had two separate trailers come out. The game is due out in late 2007, from what I've read. Correct me if I'm wrong.
[Only Registered Users Can See Links. Click Here To Register] is a link to trailer 1 - from what I understand, it is what the real-time quality of in-game play will be like, not a pre-rendered trailer. HD, Quicktime format.
[Only Registered Users Can See Links. Click Here To Register] is a link to trailer #2 also in HD, quicktime format.
Other trailers/behind the scenes documentaries about Halo 3 can be found
[Only Registered Users Can See Links. Click Here To Register]
Also, if you want a chance to Beta test Halo 3, sign up at
[Only Registered Users Can See Links. Click Here To Register]