Best Buy has buy one get one 20% off of "Prepaid Game Cards" which includes Steam, Nintendo eShop, Playstation and XBox cards. Steam summer sale is starting this Thursday and I haven't seen any other Steam card sales recently so this looks like a good time to stock up on credit.

Link to promotion:
http://www.bestbuy.com/site/promo...fer-co4272

Link to Steam cards:
http://www.bestbuy.com/site/searc...&keys=keys