Jack Skellington is one of the unannounced Disney Infinity characters that appeared in the game's original ensemble key art. He is widely expected to be available to buy before the year is out, mostly likely timed with this upcoming holiday season.
Though no picture of the Disney Infinity Jack Skellington toy has yet to surface, Disney recently released a new image of the in-game version of the character via their social media channels. The image specifically pits Jack against Jack Sparrow to see who might win. I personally prefer Jack.
There is a chance that A Nightmare Before Christmas will turn out to be a full fledged Disney Infinity Play Set with multiple characters rather than simply Jack. I am holding out hope for that.
Read more about Disney Infinity figures and toys at Disney Infinity Characters.