GamersGate currently has the PC game Just Cause 2 available for download for
only $4.99, which is 75% off the regular $19.95 price. This is one of my
favorite action games of the last couple years and I can't recommend it
enough.
Link: http://www.gamersgate.com/DD-JC2/just-cause-2
Metacritic: 84/100: http://www.metacritic.com/game/pc/just-cause-2
BTW, the game requires Steam to play.