Xbox Next (working title) and PS3 they all will appear around 2005/2006.
Sony will first be pushing their psp (gaming handheld) to compete with the game boy. There are some prototype images of this floating around the net and they us a new dics format thats about the size of a quarter and can hold about 1 gig of data.
Xbox Next will be using IBM Power PC chip, along with ATI graphics card, M$ has also stated that they will be getting into chip design, so we could see a very differnt xbox in the future, ie not based upon the PC architecture.
Game Cube, heh, sorry i cant comment on that one
it will be an intresting next few years. sony tries to compete with game boy advance and any other next gen hand held Ninteno comes out with, M$ will continue to work on the Xbox Next and sony the PS3...
i have more info but i would get killed by many people