Images from the latest Corocoro issue have leaked onto 2ch. The game is called: Pokémon Mystery Dungeon: Explorers of the Sky (空の探検隊 - Sora no Tankentai). Five 5 new starter Pokémon have been announced and they are: Riolu, Shinx, Vulpix, Phanpy & Eevee. The game is due out in Japan in the spring for the Nintendo DS.
The game is currently under development by Chunsoft. Pokémon Mystery Dungeon: Explorers of the Sky is the third game in the Dungeon series. It is currently unknown if the game will have any DSi features or if it is related to the two previous Pokémon Mystery Dungeon games Explorers of Time & Explorers of Darkness.