PSU is today reporting that the community director of Bioware has confirmed that they will be at E3. He states that they weren't happy to confirm their presence there until they "were sure that the cool stuff we're going to be showing there was set, ready and very, very cool."
While it's clear that they will be showing Mass Effect and Sonic RPG at the expo, PSU is speculating that they will also be revealing a new PS3 exclusive. Their reasoning stems from a conversation with Richard Vogel, Bioware's Director of Operations, at the GDC, during which he mentioned to PSU that there was a game in development for the PS3. Unfortunately, no further details were able to be obtained.
Checking the Bioware website, the "in development" games list shows a listing for a "new next generation game". We look forward to seeing if PSU's hunch is correct when E3 comes around.