Microsoft: Other than more info on already announced titles (QB, SO, Halo 2014), I expect at least one new first party exclude and one second or third party exclusive. I also expect a few higher profile Indies on stage; my guess: Playdead and That Game Company (I know they has close Sony ties, but they said they wanted their next title to be MP, and Chen seems to at least not hate MS, plus Spencer "Soulful" game announcement at E3)
Sony: I always find Sony's conference to be somewhat boring followed by a few big wow moments. Other than know games (U4, Order) I think well see two new first party exclusives, Sony has a large first party, time to see what they're up to. Sony will likely show off a few third party mp games like Destiny, but I don't think there will be any third party exclusives. I'm sure Sony will also rollout the Indies like last year.
Nintendo: Who knows, for good or Bad Nintendo always surprises.
As for all the other big publishers, I expect a really great showing from them. I'm most looking forward to EA, mainly due to Star Wars and Bioware.
As for games I don't think will be announced: HL3, Fallout 4, TLG