My long list of dumb predictions.
Microsoft
I predict they'll be banging the Kinect drum pretty hard. Showing more casual games, and even a few "...but don't think we've forgotten about hardcore gamers!" games as well. I think Rare will probably have a new game on display, and if Microsoft has any sense it will actually be something pretty cool and not just another off-brand Wii Sports. I suspect they'll also try and get a piece of the "free to play" market and announce something Home or Free Realms-esque.
Outside of Gears 3 they don't have much in the way "core" games on the horizion, so I imagine they'll demo that for a while. They'll definitely have a remake or some kind of update of Halo: Combat Evolved to celebrate ten years of Xbox and Halo. There will probably be a Call of Duty demo, and since Activision's got all hands on deck to get it out this fall I suspect they'll play it safe and it will look exactly like the last four. Microsoft will continue to pretend that CoD is exclusive to their platform.
Overall, I expect a fairly flaccid show from Microsoft. I hope I'm wrong though.
Nintendo
Nintendo is going to continue showing a lot of love for enthusiast gamers since they're the only ones that are still suporting Nintendo's platforms. There will definitely be a new Kirby and Pikmin game on display, and I think they'll probably announce a new traditional Star Fox game as well.
Lots of 3DS talk with a few demos. They'll have a very strong lineup moving forward.
Obligatory Zelda stage demo, and in addition to that I imagine they will announce some kind of new Zelda thing in honor of the series 25th anniversary.
Fact: Nintendo will announce a new console. It won't have a name or a release date, but I imagine they might show some impressive tech demos akin to their famous Spaceworld 2000 demo reel for the GameCube.
Nintendo could potentially knock it out of the park even harder than last year and "win" again if they play their cards right.
Sony
I have a strong feeling that Sony is going to start their press conference by showing footage from various titles (Uncharted, Metal Gear, God of War, etc.) that if you squint your eyes a bit look like PS3 games, but then will "surprise" us by revealing they were running on the NGP. Which will get a name and a price. It will be expensive.
They'll do some demos with it, and it will be a mixed bag.
I doubt the Move will be mentioned much, if at all.
They'll show off Twisted Metal, Uncharted 3, Sly 4, among others. Insomniac will reveal a new game. It won't be Ratchet or Resistance. I'm going way out on a limb with this one, but I think Rockstar will reveal Grand Theft Auto V, probably with some kind of exclusive deal with Sony. No word about Agent. The Last Guardian goes unmentioned again. I die a little inside.
Sony's press conference is going to be largley be hit or miss depending on how much or how little they focus on certain things.
Misc.
These are just random things I want to see.
Mass Effect 3!
The Elder Scrolls V.
Assassin's Creed III. Not set entirely in the present.
Deus Ex: Human Revolution.
Miyamoto (drunk) stumbles onto the stage and slaps Iwata across the face. He then yells something in slurred Japanese and leaves.
A new Rainbow Six.
Half-Life.
