It seems obvious that the next version of Android will be called, Jelly Bean, which was shown by Google when they put out jelly beans at their Android station during MWC. Now we already have an idea of what the version after that will be. According to a reliable source The Verge talked to, the same one that told them about Jelly Bean, said the next version of Android after Jelly Bean will be called Key Lime Pie.
No word yet on version numbers could be 6.0, maybe 4.2, or even 5.1. No need to worry yet about Key Lime Pie though since it is far away.
Via The Verge