Back in October 2008, Kaplan said in an interview with Curse that Patch 3.2 will contain a new raid instance that hasn't been announced yet. There's some question as to what exactly he was talking about. We also know from the article that Patch 3.3 will contain the Icecrown Citadel, so we know the 3.2 dungeon won't be that.
There is also the possibility that Kaplan didn't mean a new raid instance in Patch 3.2, but a new battleground. Many people think this is the case. Zarhym confirmed that there will indeed be a new battleground sometime in the future, and signs point this happening in patch 3.2.
Last night Crygil, a Blizzard blue poster, said that the next dungeon after Ulduar is still a secret. This makes me scratch my head and wonder if indeed there will now be a new 10/25-man raid in 3.2 or a new 5-man dungeon (or both).
As I said about we know that 3.3 will contain Icecrown Citadel, so no secret there. We know that there will be a new battleground, and that's no secret anymore. But a battleground isn't a new dungeon. So is this confirmation of a new dungeon/raid in patch 3.2?
I gather this just opens up more questions, but it's still interesting to pay attention to this now and reflect on it more when patch 3.2 actually does come around.