New York is unique because it's both a hub for numerous industries, like finance and fashion, as well as for publishing itself. This means that all the major magazine publishers are based here, along with all the big book publishers. Most of the major news networks are also based here.
LA is home to Hollywood, which means its also home to some of the premiere entertainment journalism. While the LA Times is known for having the best Hollywood coverage of any daily newspaper, all the magazines based in New York -- from Entertainment Weekly to People to US Weekly -- have correspondents in L.A. reporting on Hollywood. If you want to cover Hollywood, the movies or entertainment in general, LA is arguably a better place to be than New York, as there are jobs working for both local publications and national ones that need reporters in the thick of it.
Since DC is the seat of our national government its a mecca for political reporters. If you want to cover national politics, its the place to be. It only follows then that the local paper, The Washington Post, is known for having the best political coverage in the country. Of course you dont need to work for the Post to cover politics in DC; all the major TV newscasts and newspapers have reporters in the city. There are also myriad politically-geared publications based in DC, as well as a few national magazines. The city is also the home base of National Public Radio, which is one of the premiere radio broadcasters in the country.
A listing of some DC-based publications
Mediabistros Washington media blog, Fishbowl DC
Chicago:
Since Chicago is a major metropolitan area it also has a number of major papers and publications. Sure its home to Oprahand her production company Harpobut theres much more happening media-wise in the Windy City.
A listing of a number of Chicago-based publications
Not only is Atlanta the national hub of Delta airways, it's also Ted Turner's homebase. This means that such Turner-founded properties as CNN are based in the city. Atlanta is therefore a great spot for those interested in TV news. Since Turner's companies were bought by AOL Time Warner, a number of Atlanta media jobs can be found on AOL Time Warner's corporate job site.

