As promised, the first DLC for Modern Warfare 3 that doesn't require a Call of Duty Elite subscription will be available on Xbox Live on March 20th. It is the first of four "Content Collections" that will be available for MW3. It will bundle all the content that Elite members have already received in January and February, as well as the content in March's drop.
The "Content Collection" will include four multiplayer maps: Liberation, Piazza, Overwatch, and Black Box. In addition, the DLC will add two new Spec Ops missions: Black Ice and Negotiator. According to Activision, this is "the first time Special Ops has been made downloadable online in franchise history." Additional missions are expected for Call of Duty Elite members in May.
While the "Content Collection" will be available on Xbox 360 on March 20th, it won't be available on PC and PS3 until later--likely April, given the pattern we've seen so far. Call of Duty Elite members on Xbox 360 will be able to download March's content drop one week before everyone else: March 13.