Are you a fan of Firaxis Games or strategy titles in general? Should the answer to either or both options be 'yes', you'll definitely want to check out the current Humble Bundle offering. The promotion, which will last for another 12 days, includes the likes of Civilization: Beyond Earth, XCOM: Enemy Unknown, Sid Meier's Pirates.
As an added bonus, the Humble Bundle package of contents enables you to pay as much as you wish, though certain tiers will be locked out until you donate a certain amount ($15 is the highest tier). You can then configure how much goes to 2K Games, Humble Bundle (as a tip) and supported charities. Hit the link below to check out what titles are on offer.