Baseball-Reference.com
The website came online in April 2000.  It had originally been published in February 2000 as part of the website for the Big Bad Baseball Annual. It was first built as a web version of the Lahman Baseball Database. Now it uses a variety of data sources. It has year-by-year team pages, a baseball encyclopedia (the Bullpen, powered by MediaWiki software, using the GFDL), box scores and game logs from every MLB game back to 1954 and minor league player stats back to 1900. The Oracle of Baseball can link any two players by common teammates. The Oracle of Baseball is based on the Oracle of Bacon website.