The comic will feature “art by legendary illustrator Jim Lee and other top talents” and will “include a new story by New York Times bestselling writer Geoff Johns.” In addition, the book will also include previews of DC’s second wave of New 52 titles, including Batman Incorporated, Dial H, Earth 2, G.I. Combat, The Ravagers and Worlds’ Finest. They also say to stay tuned for “more surprises to come.”
In addition, the Free Comic Book Day site also has more information and a preview from Image 20, the 20th anniversary anthology of “six, all-new original stories promoting upcoming Image Comics titles.” Two of the titles will be Revival by Tim Seeley and Mike Norton, which you can preview on the site, as well as G-Man by Chris Giarrusso. The other stories will be announced at a later date.
The FCBD site also has previews from several other FCBD titles, including Oni’s Yo Gabba Gabba and Bad Medicine titles, and Viz’s Voltron Force, among others, so head over there if you want to check them out early.
Update: Apparently I misread the initial post and thought Jim Lee was drawing the new Geoff Johns story, but based on Brian Hibbs’ response in the comments section below, that may or may not be the case. I’ve updated the post above.