First of all, I expect to be amazed by the Nintendo Wii's game demonstrations. There are simply too many rumors and too much hype around the Wii at this year's E3. I don't have enough energy to focus on Sony and Microsoft. Sure I'll watch both press conferences live on the Internet (most of us Europeans aren't going to E3), but most of my attention will go towards Nintendo.
From Sony I expect to be amazed by the technical capabilities of the PS3, just as I was last year. Rumors are saying that the new controller will be unveiled, the boomerang was exactly what Sony said last year, "just a prototype." And of course the big bomb, the PS3 price tag.
From Microsoft? I don't really know. They don't have much to show, the Xbox 360 is out and people know what it can and cannot do. There is of course the possibility of Halo 3, which will pretty much be the only thing Microsoft can surprise us with. Some are saying that the "portable Xbox" will be shown. Highly unlikely, if you ask me.
And then there are all the games; Gears of War, Unreal Tournament 2007, Zelda Twilight Princess, Supreme Commander. I could go on and on.
I'll be watching the show(s) from the other side of the world, streaming at 300k from my place in Denmark. Only three hours until the Sony show starts. I can't remember the last time I've been this excited about E3.