Recently, GameStop announced a decent trade-in program that will allow gamers to "upgrade" from the Xbox 360 versions of select games to the Xbox One -- but it has a few provisos attached. Not only do you have to register for GameStop's PowerUp Rewards program (which has a free level), but you also have to purchase the game at GameStop itself, and you're required to buy it within 30 days of release to meet eligibility.
But Amazon doesn't have any of that. For starters, you can buy the game anywhere and still be eligible for the Amazon program. Then all you have to do is send in the game, get verified, and recieve your credit. Pretty sweet! Just be sure and read the fine print first, as it doesn't apply to every game.
One Up Your Game [Amazon]