Here's a lengthy story-related trailer for Kingdom Hearts 3D: Dream Drop Distance. Dying to learn if Sora is giving in to the darkness in his heart while Riku begins to embrace the light? Don't care as long as you get to play Three Musketeers with Mickey Mouse? This media caters to both kinds of Kingdom Hearts fans.
Edit: Disney's legal team apparently doesn't like us using the trailer that Square Enix sent us for promotional purposes. Here's a link to it on the official Square Enix Europe blog.
Square Enix has also announced some of the main voice casting for the game, as follows:
Sora: Haley Joel Osment
Riku: David Gallagher
Roxas/Ventus: Jesse McCartney
Axel/Lea: Quinton Flynn
Xion: Hayden Panetierre
Master Xehanort: Leonard Nimoy