If you watched the World Series tonight you heard the announcers discussing the Taco Bell promotion of giving away a free taco if someone steals a base. The tacos will be given away on a Tuesday between 2 and 5 PM. Either October 30 (if the base is stolen by then) or November 6 (if it's later in the series).
Get more information at the MLB website.
Note that this is not a new idea for Taco Bell, but it is the most likely to pay off.
In the 2004 World Series between Boston and St. Louis, Taco Bell offered a free taco if a player hit a 12' x 12' home run target in game 3.
In 2001, the company had a different but larger target. They floated a 40' x 40' banner in the South Pacific, offering a free taco if the plummeting space station Mir fell to the ocean in their spot.
Update: Thank you Jacoby Ellsbury!