The last few seasons, I've been updating scores from newspapers and common online sources. To fix errors in earlier data, I've been using microfiche of the Philadelphia Inquirer.
As for this earlier data:
Someone from Retrosheet provided the MLB scores.
Steven Joy has been correcting locations for the NBA lately (2010).
Someone on a mailing list from the APBR provided NBA scores before the 90s, and they came from Loren Maxwell and Dick Pfander of The Score Project.
The majority of the college football scores came from this page at James Howell's site.
Check out the site Inside Louisville, which links to my site.
College football overtime information before the 2003 season came from Scott Ferrell.
College basketball scores since the 1995-96 season came from Ken Pomeroy. Regular season college basketball scores before that came from this site.
Some conference affiliations came from here.
Canadian Football League info came from:
Official Canadian Football League site
CFL Statistics Database
Arena Football information before 2007 came from ArenaFan.com.
ABA information came from the following sites:
Remember the ABA
Steve Dimitry's ABA Web Page
The NHL scores before 1983-84 came from Stu McMurray and Jeff Wood of the Hockey Summary Project group on Yahoo.
Jeff Wood helped by getting some NHL scores from:
The Essential Blue and White Book
Chicago Blackhawks History