Baseball Library [more]
Presents general information about each team that includes history, chronology and alumni profiles.
http://www.baseballlibrary.com/baseballlibrary/teams/

Baseball Reference [more]
Comprehensive historical statistics for all players. Also offers career registers and leader boards for every major league team.
http://www.baseball-reference.com/teams/

MLB Baseball Teams [more]
Includes information on each team, history, statistics, players and stadiums.
http://www.mlb-teams.com/