I'm linking directly in these posts and not doing the normal goatse.cx paranoid stuff. Anybody providing goatse.cx links on a topic like this should be hunted down and eviscerated.

Source: C|Net News.com website.

Story lead in:

The World Trade Center houses 350 tenants within the 16-acre complex, which includes approximately 12 million square feet of rentable office space, including the two collapsed 110-story office towers, a 47-story office building, two nine-story office buildings, an eight-story U.S. Customhouse and a 22-story Marriott hotel.

Among the largest tenants is Morgan Stanley, which has its retail trading operation headquartered in the south tower of the World Trade Center.

The story also lists a couple of websites, one of which is a list of tenants that "is not clear how often" it is updated. The list doesn't appear to be responding at this moment.

Hope this helps.