Baseball-Reference.com - The most comprehensive source of baseball statistics on the internet. Information on almost every team or player in baseball history.
LOC.gov - The Library of Congress. The largest online library in the world. Millions of books, recordings and photos. Search 'Baseball'.
MLB.com - Major League Baseball Authentication program. The authenticity of memorabilia bearing an official MLB hologram can be verified on this page.
SpenceLOA.com - James Spence Authentication. Trusted third-party autograph authentication.
MinorLeagueBaseballs.com - A great source for information about minor league baseballs. Check out Tony Baseball's massive collection.
44 Pro Gloves - Design your very own customized baseball glove here.
Major League History
SportsLogos.net - Chris Creamer's Sports Logos. Huge database AL, NL, Federal League, minors, independents, international, college and women's sports logos throughout history.
SABR.org - The Society for American Baseball Research. A membership organization dedicated to fostering the research and dissemination of the history and record of baseball.
PSACard.com - Professional Sports Authenticator. The largest third-party card grading and authentication company.
ThreadsOfOurGame.com - Threads of Our Game. Database of 19th century baseball uniforms.
BaseballHall.org - National Baseball Hall of Fame. Baseball's ultimate shrine in Cooperstown, N.Y.