Information on the previously announced new Shakugan no Shana anime has finally been revealed. At first it was revealed to be just an OVA series, but then word got out that after the OVA was done, a proper third anime series would come out as well. The purpose of the OVA is to explore the characters' back stories more, before moving on to the final season for the anime. Yes that's right, FINAL season. No one's really sure why the producer's are calling it quits after the third series ends. The novels that the anime are based on are still coming out in Japan, & there's already a ton of material out there that hasn't even been animated yet. It seems weird to end things with such certainty so early on.

Similarly, it was also announced that the upcoming third season of Nodame Cantabile would also be its last. Once again, this is in spite of the fact that the Nodame manga, the original source material for the anime, is still ongoing. Season three was originally scheduled to air in the popular noitaminA block this Fall, but has now been moved to air on the block in the Winter season. So what the heck is up with Japan suddenly ending popular titles after the third season?

Source: http://www.animenewsnetwork.com/news/2009-07-08/producer-plans-3rd-and-final-shana-series-after-s-ova