Many game development studios are working on next-gen titles, but few of them had any announcements to share beyond what we saw at Sony's conference yesterday. What is certain is that Rockstar Games, best known for their Grand Theft Auto series of games, is working on a PS4 title, as their name appeared on the list of studios Sony is working with to develop next-gen games.
The studio has yet to make any formal announcements regarding its plans for the next generation, and Grand Theft Auto V itself has only been confirmed for release on the Xbox 360 and PlayStation 3, with no PC, nor next-gen version in sight.
It's entirely possible, of course, that the studio will announce a next-gen version of the game to coincide with whatever PC version they have planned. After all, confirmation of the PC version for games like LA Noire and GTA IV didn't even arrive until after the console versions were released.
As for what they have planned for the next-gen—assuming it's not GTA 5—the only real possibility is a sequel to Red Dead Redemption or Agent, a game originally slated for release on the PS3. Curiously, the company has a page up for Agent, which lists PS3 as its only console. Unless they plan on making a new Max Payne or Midnight Club title—both of which were far less popular than RDR, the smart money's on Agent or a new IP.