Activision have released a full list of perks you get by subscribing to Call of Duty: Elite - the premium service that tracks your performance in Call of Duty games. Most of Call of Duty: Elite is included for free with Call of Duty: Modern Warfare 3, but there are premium perks and these have now been listed on the official site.
Included in the list is free DLC (twenty in total), but it's unclear whether this applies to map packs or if this is something else. There are also special perks for those who pre-order Call of Duty: Elite and become "founding members". Anyway, click the link above for a full list.