It seems that a sequel to the ongoing Gainax anime adaptation of Nisio Isin’s shounen manga, Medaka Box (めだかボックス) has been confirmed via a tweet from cyan3. The source seems to be outdated (tweeted September last year), but it mentioned the series having two installments, the first being sometime in April 2012 and the second one around September of the same year. There’s no official announcement from Gainax’s Medaka Box main website as of today, but an update will be given as soon as it’s out.
The manga version is currently running and has around 15 tankobon volumes and more than 150 chapters. With so much material still available, and enough market appreciation, it is unlikely that the anime series would come to an end too soon. Nisio Isin (or NisiOisiN) has been a popular name for the Bakemonogatari and Katanagatari series, both of which had anime adaptations for the past years.