Saw this on Gizmodo - go to www.greenmangaming.com and use the voucher code GMG35-5BRU6-ZDRX7 on the checkout page. This is the lowest price I've seen it. Activates on Steam. Not sure how long it'll be good, but it's working today as of 7:57 PM.
(I think this code is only good for XCOM, I tried it on GW2 and it wouldn't take it.)
(I think this code is only good for XCOM, I tried it on GW2 and it wouldn't take it.)