EDIT: The 24 hour sale is over,
Civ 5 is $11.98/8.99€/£5.99 from Greenman Gaming for 24 hours. You can use a referral link to get $5 store credit back,
You receive a Steam Serial key in the mail, long live the age of digital distribution, 20 minutes later i was playing.
The following link should give you a 5$ refund in your store wallet after purchase to spend on other stuff like a copy of magicka wich is exactly 4.88 atm
Following the link does not give any feedback as far as i could see that you will get the refund, it just works.
updated: Referral link: http://www.greenmangaming.com/?gmgr=zexuhubo