Bing has a promo right now only good thru 10/15/15, for free $5 Xbox gift card. You have to sign up for Bing rewards. I'm not a MS whore and I'm not licking their buttholes. I just thought I should share for everyone who isn't willing to buy the cool stuff. Like me.
Edit: It seems if you already have Bing rewards its possibly not available. However maybe make a new account and send the card code to an alternate email? "Welcome to Rewards" is what you're looking for.
Have to be in the US, also. I don't control Microsoft, sorry :(
Edit 10/16: Some comments are reporting that its still available. Promo supposedly ended 10/15. Check it out if you want to.