Seems strange to have an E3 thread without anyone wondering if LA Noire, GT5 and Duke is going to be there. Anyway my guesses,
MS
Loads of Kinect stuff both core and casual, shows some of the stuff from TGS last year.
Forza 4 being the real definitive driving game this gen,
Halo remake
MW3 stuff
Gears 3 new features
Possibly the insomniac multi-plat game
Hints on new Xbox
Some Gold and US only features again.
Windows mobile 7 stuff
Skype intergration with XBL/kinect coming later
Ninty
Some 3DS games, Mario Kart, and Some kinda Mario World game
Loads on project cafe/stream not a big leap over PS3/360 but a big leap from the wii. Will have some cool features and perhaps uses the vitality sensor, intergrates with the 3DS. Shows some demo footage of some hardcore 3rd party games for the Wii2, possibly MW3 or some Rockstar game.
Sony
NGP stuff games look good, price for wifi only reasonable 3G version too high.
PS3 move sorcery, some 3rd party casual stuff and a new IP for move.
Uncharted and Resistance 3 stage demos
Starhawk shoing the space battles
Heavenly sword 2 done by santa monica
Some new features that probably no one rarely wants but are quite cool, still no x game chat.
Agent shown (lol)
Some 3rd party exclusive stuff, perhaps for BF3
Few new 1st/2nd party games
Gives everyone a $50 PSN card even though the store still isnt up