Halo 2 is presumed to be released Fall/Winter 2003, but personally I would suggest the release date of 15 Novemeber 2003. See, that would make a sort of pattern:
15 November 2001: Xbox Launch Date
15 November 2002: Xbox LIVE Launch Date
15 November 2003: Halo 2 Launch Date (??)
It would be cool, because the release of Halo 2 will be one of the most important ones, because it is the sequel to the No.1 Xbox game. It would also be the last day of the Xbox LIVE subscription, for whoever buys it this Friday.