Amazon offers Prime members a Microsoft Xbox Live 3-Month Gold Membership Card for $12.49 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $4.98.) That's $6 under our August mention and the lowest price we could find now by $6.
Want an extra month? Best Buy offers a Microsoft Xbox Live 3+1-Month Gold Membership Card for $14.99 via in-store pickup.