Jump Festa 2012 (ジャンプフェスタ2012) is being held at Makuhari Messe in Japan December 17th and 18th and a booth at the event has revealed the new game
Pokémon + Nobunaga's Ambition (ポケモン+ノブナガの野望). The game will be released on the Nintendo DS in Japan in 2012 and it is a RPG crossover game between Pokémon and
Nobunaga's Ambition. The game takes place in the Ranse Region.
An imageboard thread of pictures from the booth has been created.
Click on images for higher resolution
Sources:
http://www.pokemon.co.jp/ex/ranse/pre/,
https://twitter.com/#!/dengekionline/status/147829851750006784 and
http://www.4gamer.net/games/145/G014507/20111217005/