As Amy & I mentioned back in August, we recently purchased Ticket to Ride, a boardgame for 2-5 players that involves building collections of train routes on maps. (Not familiar to Ticket to Ride? Learn more via the official website!)

Mystery Train expansion was introduced in 2004
The game won the 2004 Spiel des Jahres, which is somewhat like the Academy Award-equivalent for boardgames. That same year, the first expansion for the game, Mystery Train, was released.
The expansion was originally available for free at game trade shows and via magazine inserts. The maker of Ticket to Ride, Days of Wonder, also sold it for a short time via their website. Eventually the expansion went out-of-print, but then was made available as a PDF download on their website. I printed my set on some card stock and it has worked out well.