We can look forward to 4 maps, not 3 as is the norm. Supposedly, if you play on the 360, you will have to pay for the content. Infinity Ward has not decided yet how they will release the content for PC as PC users are use to getting maps for free.
The 4 maps will be Broadcast, Creek (Pictured Below), Kill House, and Chinatown.
Broadcast is carried over from the single mission game but is said to be expanded and modified. It is mostly indoors with 2 floors, but you can also access the roof and parking lot which has been expanded to include another small building. Broadcast will be the only map carried forward, the 3 remaining maps will be completely new and said to be totaly non middle east, non russian locals.
Creek is said to be a very large outdoor map with a line of buildings/houses on one side. A deep rocky creek that circles and crosses the middle of the map with alot of bush on its rim for snipers to blend in. It is also said to have a lengthy winding cave system and a waterfall.
ChinaTown, not much information has been given on this map, but the name pretty much says it all.
Kill House, this is said to be a bonus map and was not showen nor any further details released about it other than its name. Except for this Quote " think of the single-player campaign's initial training level as a reference." So you can probably assume lots of plywood and card board cutouts of bad guys.