This third title is called The Grinder, and is a four-player co-op shooter for the Wii, where players must battle waves of vampires, werewolves and the undead. So, yes, Left 4 Dead with friend codes. It's currently scheduled for a "holiday 2010" release.
As for other details, the announcement interview is heavy on suggestion, light on facts. Guess we have to wait until E3 next week to learn more.
The Grinder Revealed [IGN]