It's starting to sound like world famous developmer/publisher Rockstar Games isn't resting on the success of its recent hits. In fact, one analyst believes they may be currently working on five separate projects.
Wedbush Morgan analyst Michael Pachter wrote in a post-E3 note that he believes each of Rockstar's five studios have their own game in the works. Which, presumably, includes Grand Theft Auto V.
He also said that due to their parent company's revenue expectations, we can expect one of these titles to launch by the end of their fiscal year in March 2013. Given that the only game announced yet is GTAV, that gives us a pretty good idea of when to expect its release.
As for what the other titles might be? We haven't a clue. However, given the success of Red Dead Redemption in 2010, you can bet your socks they're working on a follow up. One of the other titles may also be the oft-delayed, potentially next-gen title, Agent.