Major League Soccer is considering expansion by at least one if not two teams next year. Here is a handicapping of the possible expansion.
I think Seattle and Philadelphia are good shots. Seattle has a solid franchise for United Soccer Leagues and strong fan base, including the Vancover area. I think MLS would be silly to ignore that location. Philly has been abuzz with rumors of a soccer specific stadium in the redeveloped Chester area (just south of the Philly airport and city proper) and that could be great for the area.
St. Louis has long been a great soccer city and would also be a solid choice and I like the idea of some more teams in teh middle of the country as opposed to just the coasts. I don't want to see another franchise in New York at all. The Red Bulls are doing well and unlike LA and Chivas USA, a sort of off shoot of a popular Mexican club, I am not sure New York can really support a second team just yet.
Barring a merger between USL and MLS in the near future, here are my preferences
2. St. Louis
4. Atlanta--a real long shot I know.