First off, Factor 5, the developers of the forthcoming dragon shooter Lair, has already confirmed that a demo will be coming out for the game "in July", one month before the game's official August 14th release.
Another demo rumored to be making the rounds "very soon" is Ninja Theory's Heavenly Sword, featuring a sweet-looking hottie battling all kinds of impossible odds to bring down the man that murdered her father. Theory should be finishing up work on this soon and already promised a demo would be coming as well. So, again, it would be a big part of some kind of online E3 push.
And let's not forget the online betas, either.Word has it that Little Big Planet would be starting up a beta as well. Again, E3 could hold the key to all this and Sony could really give its users something spectacular if it wanted.