Some possibilities:
Conservative MLB Realignment (expansion: Carolina + Nashville)
American League
East: Baltimore, Boston, New York, Toronto
North: Chicago, Cleveland, Detroit, Minnesota
South: Houston, Kansas City, Nashville, Texas
West: Arizona, Los Angeles, Oakland (LV?), Seattle
National League
East: New York, Philadelphia, Pittsburgh, Washington
North: Chicago, Cincinnati, Milwaukee, St. Louis
South: Atlanta, Carolina, Miami, Tampa Bay
West: Colorado, Los Angeles, San Diego, San Francisco
Conservative MLB Realignment (expansion: Montreal + Carolina or Nashville)
American League
Atlantic: Baltimore, Boston, New York, Tampa Bay
East: Cleveland, Detroit, Montreal, Toronto
Central: Chicago, Houston, Minnesota, Texas
West: Arizona, Los Angeles, Oakland (LV?), Seattle
National League
Atlantic: Miami, New York, Philadelphia, Pittsburgh
East: Atlanta, Carolina/Nashville, Cincinnati, Washington
Central: Chicago, Kansas City, Milwaukee, St. Louis
West: Colorado, Los Angeles, San Diego, San Francisco
Geographic MLB Realignment (expansion: Carolina + Nashville)
Atlantic: Baltimore, Boston, Miami, New York, New York, Philadelphia, Tampa Bay, Washington
Eastern: Atlanta, Carolina, Cincinnati, Cleveland, Detroit, Nashville, Pittsburgh, Toronto
Central: Chicago, Chicago, Houston, Kansas City, Milwaukee, Minnesota, St. Louis, Texas
Pacific: Arizona, Colorado, Los Angeles, Los Angeles, Oakland (LV?), San Diego, San Francisco, Seattle
Geographic MLB Realignment (expansion: Montreal + Carolina or Nashville)
Atlantic: Boston, Miami, Montreal, New York, New York, Philadelphia, Tampa Bay, Toronto
Eastern: Atlanta, Baltimore, Carolina/Nashville, Cincinnati, Cleveland, Detroit, Pittsburgh, Washington
Central: Chicago, Chicago, Houston, Kansas City, Milwaukee, Minnesota, St. Louis, Texas
Pacific: Arizona, Colorado, Los Angeles, Los Angeles, Oakland (LV?), San Diego, San Francisco, Seattle
For those of you who are more graphically inclined, the same realignments above but in image form: