Xbox Live has already started discounting games and digital trinkets for this big shopping week. Most notably, Spelunky and Rock Band Blitz are down to 600 Microsoft Points each. You should probably buy those, particularly the former if you're looking to get some local multiplayer going on Thanksgiving.
Major Nelson has posted the full list, which is good until Monday, November 26. All told, this is an eclectic group with stuff like Forza 4 content packs, Sega Vintage Collections, and male-only Avatar gear. Those who are only now getting an Xbox 360 might be able to find some good deals in here beyond my aforementioned recommendations.
Xbox LIVE Marketplace Holiday Offers [Major Nelson]