It's been revealed that the the next original animated movie from DC will be Justice League: Throne of Atlantis. The title of the film was revealed on the back cover of the Batman: Assault on Arkham Blu-ray. You can see that cover art below, which comes from Worlds Finest Online.
I've been enjoying the recent animated films from Warner Bros. Home Entertainment, DC Entertainment, and Warner Bros. Animation. There's no official information on what the story of the next movie will entail, but you can expect more details and other information on the next slate of DC Universe animated movies at San Diego Comic-Con in July.
We'll be there to cover all this, so stay tuned for further coverage on films such as Batman: Assault on Arkham, Justice League: Throne of Atlantis, and whatever else is announced.
Here's some story information from the comic book that will serve as the base of the upcoming animated film:
A Navy warship incites the wrath of the Atlanteans after its missiles malfunction during a test and end up attacking Atlantis. Ocean Master, the new king of Atlantis, declare war on the surface world. While they are in a café in Metropolis, Superman and Wonder Woman are forced to suit up and stop an aircraft carrier from flooding into the city and killing thousands of people. In the battle that follows the Justice League is captured, save Cyborg. He realizes they need help and calls in help from Green Arrow, Hawkman,Zatanna, Firestorm and more. The Heroes stop Ocean Master and figure out that Aquaman's assistant Vulko was behind the bombing so Arthur would take the throne once again.