As the title says. Each player is listed with the team on which he played the most games and the first and last years of his career. Data is from 1876-2010, though some players may be active in 2011.
The number before the colon in each pair is how many games in which they both hit at least 1 HR while on opposing teams. The years listed for players who played in both the 1900s and 2000s are truncated for space reasons (e.g., 1995-10 = 1995-2010). See first comment for team/franchise abbreviations.