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.