Hardcore Gamer is giving away 60 codes that double the amount of credits you get from pickups in Warfare for 3 days.
Head over here to enter:
http://www.hardcoregamer.com/2015/08/13/giveaway-warframe-3-day-credit-booster/162499/
Head over here to enter:
http://www.hardcoregamer.com/2015/08/13/giveaway-warframe-3-day-credit-booster/162499/