Take Two and Firaxis have announced that Civilization V will feature Steamworks functionality and achievements on Steam. All versions of the game will feature Steamworks. They have also announced plans for Digital Deluxe edition of the game available on Steam. The digital deluxe version will add the Babylonian civilisation and their ruler Nebuchadnezzar II, as well as a "Behind the Scenes at Firaxis with Civilization V" video and a copy of the soundtrack.
If you pre-order the regular or digital deluxe version of the game on Steam you will also receive a map pack on the release day free of charge.