This deal doesn't appear to be part of the Xbox Live Gold Weekly deal, but it's a deal only available this week none the less. Right now you can snag the totally awesome Gears of War 2 All Fronts map pack for only 400 
. The pack, when released, originally cost 1600 .
So why the sudden change in price? It's to celebrate the Games on Demand release of Gears of War 2. What's included? 19 multiplayer and Co-Op Horde mode maps as well as the new cut campaign content that's available to play in co-op. You can check out some impressions of the content here.
Remember, you only have until October 18th to get it at the 75% off price!
Source: Marketplace.xbox.com