I bet you didn't know the original Halo had a subtitle of "Combat Evolved" did you? Well now you can learn all about Master Chief's first mission for only 600 MS Points, that's $7.50 of your Earth money. The game features 2 player local co-op play through the entire story so you and a buddy can team up to kick some Covenant butt.
Seriously, if you've never played the original, now's the time to do it. I still crack my copy out from time to time.
You can purchase the game right here or via your Xbox 360 console. A gold account is required to get the discount.