http://www.xbox.com/en-US/live/rewards?xr=shellnav
Here's a heads up for 360/Xbox One owners. I didn't know about the Xbox Live Rewards program until I saw an IGN article about it yesterday so I figure some other people here might not have heard of it either. Basically it's a free program that gives you credits for doing things you probably already do. Each time you earn 5000 credits it is automatically converted into $5 and added to your account for use on the Xbox Live Marketplace. Here is a page that explains some of the ways to earn credits
http://rewards.xbox.com/mymissions/
I rent and buy games at discounted prices later so I probably won't earn as many credits as some people here. I should still be able to earn a decent amount though. For example, if you preorder the big fall games from the Microsoft store you earn 15,000 credits for each game. That equals $15 in store credit for future purchases. I don't preorder games because I can download anything I want on day one without paying up front. However, The Master Chief Collection was a no brainer day one buy for me anyways. Now I will preorder and take the $15 worth of credits.
You also get credits in other ways that don't cost you any money. If you download the free Games with Gold games and play them for 10 hours that's 1000 credits. You also get credits for earning achievements to increase your gamerscore but I'm not clear on how much you earn for that. It's a cool little program that I wish Sony would steal from them because I spend way more time on their systems.