GDC is only a couple weeks away now, and with the role of E3, being downgraded this year, instead of getting bigger every year, developers have a bit smaller venues and chances, to make a media splash.
I'm guessing we'll see:
Colin McRae Dirt in Action
Toca for 360 will be announced
Forza 2 gameplay vids
Sega Rally will get some notice.
The Club will release some media/screenshots
Command and Conquer will be running at the event on 360's
Marvel MMORPG will show off some early screens
Gears of War will get a new Map Pack 2
More of Lost Odyssey will be shown, delay will be announced
tons of Mass Effect stuff
Tons of Too Human stuff will be shown
Next GTA will be shown behind closed doors.
Splinter Cell that is exclusive to 360, will be shown
And no news from Halo 3, only behind closed door gameplay and vids. Beta will release sometime in May.
Command & Conquer will get a demo on marketplace
Xbox Live Arcade will get a few more announced games... One will be a Trivia type game you see played in pubs/bars.
these are just all total speculation, but fun till we see what really happens
Wie ich's hasse wenn's wieder einmal "geschlossene Gesellschaft" einer Spielevorführung heißt. Das haben die bei Mass Effect und Bioshock abgezogen und uns die (arg gekürzten) Präsentationen erst viele Wochen später gezeigt. 
