Tales of Graces uses DS download play to transfer Kamenin Merchant, a portable dungeon crawler to the DS. For a downloadable mini-game, Kamenin Merchant is rather impressive. It generates random dungeons, has a four player mode, and transfers items back to Tales of Graces.
Kamenin Merchant is so big Namco Bandai decided to sell it as a downloadable DSiWare game. A price, release date, and details about potential Tales of Graces connectivity have not been announced, but if you have a Japanese DSi you will be able to play Kamenin Merchant at some point.