Green Man Gaming is offering Civilization 5: Brave New World expansion for $20.25 with voucher GMG25-GDSAK-7FPWQ.
http://www.greenmangaming.com/s/gb/en/pc/games/strategy/sid-meiers-civilization-v-brave-new-world-na/
Other titles available: http://blog.playfire.com/2013/05/remember-voucher.html