NOTE: This offer is for Silver Members ONLY. This will not work for current Xbox Live Gold Members.
1. Click "Get 1 Month Free Now" at bottom right of page.
2. Sign into your Xbox Live account via Windows Live.
3. Enter Credit Card or PayPal info.
4. Turn OFF "Auto-Renewal" via Account Settings
5. Enjoy 1 Free Month of Xbox Live Gold
I used this myself yesterday, and 3 other friends of mine. I don't know when this promotion will end so jump on it ASAP!