There will be several new game announcements, including a new game from Rare.
Alan Wake will be there, probably a trailer or a technical demonstration.
Gears of War will be there with emphasis being put on the gameplay in the solo campaign and the co-op/multiplayer side of the game.
Bungie will announce a new IP, hopefully it' ll be online focused.
Ubisoft
may announce The next Ghost Recon, but then they may wait until after RB6, SCDA and the (MIA) PS3 version of GRAW.
Mass Effect will be there, and hopefully we' ll see some new gameplay footage.
Huxley will be there, probably playable.
Call of Duty 3, Brother in Arms 3 and Medal of Honour: Airbourne could be there, ...at leat one of them will. If one was to be missing i' d say it' d be MoH, and CoD3 and BiA3 are much closer to release.
Other stuff i' d like to see are; Ninja Gaiden 2, Resident Evil 5, Alone in the Dark, Killer Instinct 3, After Burner, Shenmue 3/Trilogy etc...
As for demo' s, i' m hoping for either a RB6 or SCDA multi-player demo!