By using Bing as your search engine (and yes, it's not terrible), you can earn Microsoft Rewards points.  Then, you can redeem them for a 1, 3 or 12 month Xbox Live Subscription.

Just sign up for the Microsoft Rewards Program and search while logged in to your Microsoft account and you can earn up to 500 points per day.  Then, after you reach the amount need to buy your Xbox Live subscription, just go to the Rewards web site and redeem the points to get your code.