Steam users can snag Civilization 5 and its Gods and Kings expansion for $7.49 each, while the Civilization 5: Game of the Year Edition is available for $12.49. The Game of the Year Edition includes the original game, all four Cradle of Civilization map packs (Americas, Asia, Mediterranean and Mesopotamia), the Babylon Civilization pack, the game's official soundtrack and a handful of additional Scenario packs including ones for Spain, the Incas, Polynesia and Denmark.
Civilization 4: The Complete Edition is also available for $7.49 and includes the original game as well as the Warlords, Beyond the Sword and Colonization packs. All three expansions are also available individually for $1.24, $2.49 and $4.99 respectively, while the standalone Civ 4 costs $4.99.
Civilization 3 Complete is also available on Windows PC for $1.24. All other games and expansions are available for PC as well as Mac.