The Philadelphia Athletics Historical Society - A great organization that you can visit online and in person
1911 Athletics Wikipedia Page
Society for American Baseball Research
Retrosheet - "Retrosheet was founded in 1989 for the purpose of computerizing play-by-play accounts of as many pre-1984 major league games as possible."
Baseball-reference - The most addictive website ever
Fangraphs - The second most addictive website ever
The Baseball Biography Project - Learn the stories behind the players.
Twitter - Yes, god forgive me, I got a twitter account for this site.