Wizards of the Coast announced that the Magic: The Gathering Lorwyn set will include the first of a new card type--planeswalkers (see 'WotC Plans Magic Game Day'). The cards will introduce a new aspect to the game by featuring characters who travel between planes and settings. 

Planeswalkers were introduced in the Magic fiction line, but the specific characters in the game are new and will only appear in upcoming stories.  WotC describes the planeswalkers as somewhat more interesting characters that are a little more powerful and can perform new options. 

Lorwyn is slated for an October 12th release.