UPDATE: Superhero Hype's live blog of the Warner Bros set of panels has just confirmed that the Man of Steel sequel will be a team-up of Batman and Superman.
The announcement featured the Batman/Superman logo (the Man of Steel logo with the Bat symbol behind it), and a quote from The Dark Knight Returns (""I want you to remember Clark," he says, "in all the years to come. In all your private moments. In all the years to come, my hand at your throat. I want you to remember, the one man who beat you.")
Original: The Los Angeles Times reports that Warner Bros is expected to announce the follow-up to Man of Steel today at the San Diego Comic-Con, which will be released in 2014. The plan is for that film to be Superman/Batman. Zack Snyder would direct, David S. Goyer would return to write and Henry Cavill will play Superman again. It's unlikely that Christian Bale will be back as Bruce Wayne/Batman.
A Warner Bros. spokesman would not comment on the rumors.
Christopher Nolan is expected by some to produce the new film, but it's unknown how involved he will be.
This goes along with a new comic series featuring the two heroes, as Greg Pak and Jae Lee are working on Batman/Superman for DC. The two have teamed up several times in the comics and even have been adversaries at different points (most notably, The Dark Knight Returns).
Meanwhile, The Hollywood Reporter adds that there are tentative plans for a Flash movie in 2016 and a Justice League movie in 2017.
411mania
If they can't get Justice League together in time, I guess this'll do for now! It's Superman/Batman vs. Avengers 2 in 2015!