I will say Sony, I think they will try and make up for last years bad showing and how MS stole the spot light. I expect new videos and details of all of their big 1st party games for both the PS3 and PSP.
Information on the downloadable music video service they have been talking about, plus WW access to their Video Store in the PS Store.
A firmware update detailing in-game chat, cross game invites and multiple user login.
A couple of new game annoucements, and possibly some hardware related annoucements.
But I do stil think that Microsoft and Nintendo will have good showings as well. Microsoft will have a tough time matching what they did last year, but Nintendo can walk on the stage and say "Were making a new Zelda game for the Wii" and walk off and it would be better than last year.