Halo: Reach in some form or another. But if for some crazy reason you just got an Xbox 360 and you're still missing out on Bungie's swan song to the Spartans, Microsoft's got a digital version of the game discounted alongside all of its DLC (well, most of it, anyway -- the Anniversary Map Pack is sadly absent).
There's also a handful of Avatar clothing/items, as well as the always thrilling "Anchor 9 Premium Theme," you big collector, you. Head to Xbox.com's Halo: Reach section to see how today's discounts apply to your region.
Should Halo not be your particular bag, a whole mess of other deals are being offering in the coming days and weeks, mostly of the Hasbro variety. Major Nelson has conveniently compiled them for you right here.