According to this video, the map names "Shipbreaker" and "Terminal" briefly appeared in the map selection list of Modern Warfare 3's private match menu, apparently tipping off the names of two maps to come in the game's next DLC drop this month.
The enthusiast site CallofDutyMapPacks.com speculates that "Shipbreaker" could be a new Face Off map, similar to Rust from Modern Warfare 2. It may also end up going by the name "Boardwalk". "Terminal" was the name of a map in Modern Warfare 2 as well, and rumours have circulated that it may be returning in MW3.
I've pinged an Activision representative for the obligatory comment.
Leaked June DLC: New Map Shipbreaker & Terminal on their way [CallofDutyMapPacks.com — thanks Alex and others!]