Xbox.com is now hosting the Halo 2 trailer as was promised, though you will need to install Windows Media Player 9 to get it from that site. There is a Quicktime version on Halo.Bungie.org.

Update: Here is the FileShack mirror of the WMV file, and here is a copy of the QuickTime version. Note that we're still doing without a few servers on FileShack, so your download might take a few minutes to start.