The most recent city to have two championship winning teams in the same year was...Boston, in 2004 (Sox and Pats).
Here are all of the cities in North America that have ever had two championship teams in the same year:
http://www.nuttyaboutsports.com/nort...e-champs.shtml
Not very many, and even fewer if you only count the "Big 4" leagues (MLB, NBA, NFL, NHL).
If you only include those 4 leagues, since 1967 (NHL expansion and the start of the Super Bowl era), it's only happened 4 times: 1969 - NYC (Mets & Jets); 1979 - Pitt (Steelers & Pirates); 1988 - LA (Lakers & Dodgers); and 2004 - Boston.