I have a Silver Account, and when I signed into the dashboard and saw the ad to get 2 Months of Gold for only £2!
Its on for 48 hours only, so be quick!
To turn off auto-renewal for your Xbox LIVE Gold Membership:
Go to http://www.xbox.com/accounts
Link opens in new window.
Click Sign In (upper-right corner) and type your Windows Live ID information (if you’re not already signed in).
Next to Automatic Renewal, click Change.
Change your automatic renewal setting to OFF
*UPDATE* You may also use Paypal as a preffered payment option!