Collector Websites:

Pete Rose - All things Pete Rose.
Mark Grace - Described as "a website by a devoted fan...for a player devoted to the game".
Frank Thomas - Dedicated to collecting Frank Thomas cards and memorabilia, by Chad.
Will Clark - The definitive Will Clark collection.
Ryne Sandberg - The Ryne Sandberg collection.
Don Zimmer - A Don Zimmer Fan Site.
Crusade Collectors - Collecting The 1998 Donruss Crusade Insert Set & Information Regarding The Set.
Card Magnet.

Discussion Boards:

Freedom Cardboard - Forum for sports fans.
Beckett Media - The #1 source in the hobby.