Looks like Bethesda Softworks http://www.e3expo.com/exhibitors/92/exhibitor-list/. I wonder if they'll be showing off just Brink and Fallout: New Vegas, or TESV as well? A man can dream...
Going by the little information we have: that for the last year most of Todd's time has been dedicated to revamping their engine; and that the trademark for Skyrim must be used by August of this year, my money is on the following:
1) Brink is the game with the most show-time, probably with playable booths.
2) New Vegas has gameplay footage shown but not playable to the press and public, similar to Oblivion at E3 2006.
3) Todd's "next big game" is revealed with a teaser trailer, similar to how Brink was unveiled a couple of days before the E3 of last year.
That covers all the bases a developer could ask for. Gameplay available for an imminent game, Gameplay footage for a game with a huge hype metre, and a teaser to start a brand new hype train (for all those gamers that don't lurk in this section of Beth's forums)
Chances are that it is TES:V. Chances are that it will be announced, and we will get the confirmation that we've all been asking for. Chances are that we've all been lying about how confirmation of the game's existence is all that we're after, and the forums will be full of complaints about how little information we received about TES:V at E3.