AbandonGames
Offers a search engine for classic games and an active forum. http://www.abandongames.com/
Regular Links:
Abandonwarez: The pros outweigh the cons
Article on abandonware from The Adventure Collective.
http://www.adventureclassicgaming.com/index.php/site/features/160/
Dan's 20th Century Abandonware
Application software from a time not quite forgotten.
http://www.dans20thcenturyabandonware.com/
Free Oldies
Search engine covering many sites. Search by name or sort by genre.
http://www.freeoldies.com
Macintosh Garden
Dedicated to preserving abandonware games for the Mac OS.
http://mac.the-underdogs.info/
The Abandonware Ring
The original Abandonware Ring. With a FAQ and a resources section.
http://www.abandonwarering.com/