Eurogamer has a
nice list of
Halo 3 rumors up today. They include the possibility of 50 person multiplayer (reasonable given that Perfect Dark: Zero is expected to support that many), online co-op over Xbox Live (hopefully but doubtful given the lack of support of this in the past) and will feature a grittier plot line (hopefully resolving the open plot lines from
Halo 2). There's some other information there but most of it seems like fan boy hype at this point, especially given that the game hasn't been officially announced yet.