The cities and teams (note that "Metro Population" refers to the Census Statistical Area population- these extend further beyond the city limits and give a better idea of actual markets). Add ideas for names if you have them.
Louisville, Kentucky (AFC East)
Metro Population: 1,522,112
Any time people talk about either of the major 4 sports leagues expanding, Louisville is always in question. The metro area is home to 1.5 million people, without a single major professional sports team. The city has a rich sports history, and is home to the University of Louisville, whose teams enjoy a strong, loyal fanbase in the city. Additionally, there is already a 61,000 seat stadium for the University of Louisville, which could be used until a new stadium for the team could be constructed.
Potential Names: Stallions, Generals, Colonels
Omaha, Nebraska (AFC North)
Metro Population: 931,666
Located about 2 hours north of Kansas City, Omaha is a rapidly-growing city. It is known as the "Amateur Sports Capital of America", as it is home to the NCAA College World Series, the US Olympic Swimming Trials, and the Creighton University men's basketball team. Omaha is also located close to the University of Nebraska in Lincoln (about 1 hour), and would attract a following from across the entire state. A rivalry would most likely develop with Kansas City, as well as with Green Bay, based on existing college rivalries. Would require the construction of a new stadium.
Potential Names: Locomotives, Locos, Spikes, Thunderheads
Mexico City, Mexico (AFC South) [Wrong Location on Map]
Metro Population: 20.9 Million
Recently, the NFL has been focusing intensely on Mexico for international expansion. Throughout the country, the NFL has a fairly strong following, and would be much more logistically practical than a team in London. The team would be based at Estadio Azteca. There is currently a professional football league active in Mexico, called La Liga de Futbol Americano Profesional (LFA), which the NFL could ally with (much like they tried to do with the AAF), in order to create sort of a minor league to expand the popularity of the game across the country.
Potential Names: Aztecs, Capitolinos
Oklahoma City, Oklahoma (AFC West)
Metro Population: 1,396,445
Another rapidly-growing city, with a strong football presence. Fairly strong support for the Texas NFL teams, as well as the college teams at the University of Oklahoma and Oklahoma State University. There currently are some areas located in the downtown area where a stadium and the related development could be constructed. A rivalry would most likely develop with Kansas City, Denver, and other AFC West teams, as well as the Texas NFL teams.
Potential Names: Barons, Oilers, Pronghorns, Outlaws, Gunslingers
Norfolk/Virginia Beach, Virginia (NFC East)
Metro Population: 1,833,136
Another major city (actually the largest in Virginia), that lacks any major professional sports teams. There has been talk of expansion into this market by the MLB and the NBA, as well as the NFL. A team located in Norfolk/Virginia Beach could also draw support from the rest of the state, besides that which is considered part of the DC Metro Area, as any teams located in that area are branded as DC teams, not Virginia teams.
Potential Names: Neptunes, Tridents, Tritons, Navigators, Commodores, Destroyers, anything having to do with sailing or the Navy.
Quad Cities, Iowa/Illinois (NFC North)
Metro Population: 383,681
An area that would, at first look, be easy to overlook. However, the team would draw a following from the nearby cities of Iowa City, Cedar Rapids, and Waterloo, as well as Des Moines. College football has a strong presence in Iowa. Rivalries would most likely develop with the Omaha expansion team, as well as with Chicago and Green Bay. The stadium itself would be located in Davenport, Iowa, as it would be much more likely for the team to draw support from Iowa if it was actually based in Iowa.
Potential Names: Aggies, Reapers, Harvesters
San Antonio, Texas (NFC South)
Metro Population: 2,473,974
A city in the heart of football country with a pre-existing NFL-capable stadium.
Potential Names: Vipers, Venom, Blazers
Portland, Oregon (NFC West)
Metro Population: 3,239,335
Portland is also frequently talked about when considering expansion for the major sports leagues. Rivalries would most likely develop with the Seahawks and with the 49ers.
Potential Names: Lumberjacks, Pioneers, Axmen
Toronto, Ontario (NFC North)
Grand Rapids, Michigan (NFC North)
Orlando, Florida (AFC South instead of Mexico City)
Memphis, Tennessee (AFC South instead of Mexico City or Orlando)