Baseball-Reference.com
Find up-to-date major league baseball statistics for each player, team, and league in baseball history. Includes batting, pitching and fielding stats along with leaders, managers, links, books and award winners.
http://www.baseball-reference.com/

USA Baseball
Official site of the national governing body (NGB) for the sport of baseball. Includes news, events, teams, photos, videos, and newsletter.
http://web.usabaseball.com