Xbox Live Marketplace offers an Xbox Live Gold 1-Month Subscription for $1. (You'll need to login into your free account to see this offer). That's tied with our March mention at $9 off and the best we've seen for a 1-month subscription. It's only valid for free accounts and not current Xbox Live Gold Members.
Note: Your subscription will automatically renew at the end of the month and you'll be charged the current regular price so be sure to turn off auto-renew if you don't plan on keeping the subscription.