Source: NolanFans via WB Exhibitor site
This comes from NolanFans:
he third trailer for The Dark Knight Rises will be attached to Marvel’s The Avengers on May 4th. Both 2D and 3D conventional showings of The Avengers (as well as 2D and 3D IMAX showings!) will be playing the trailer. Read more: http://www.nolanfans.com/2012/04/20/third-dark-knight-rises-trailer-with-the-avengers/#ixzz1smO2HSr5
Sounds pretty cool. if it shows here in the UK, it'll be the best thing ever. We'll see come Thursday night.
Check out NolanFans for a screenshot of the actual announcement.