Ebay Auctions (with international branches)
Game Trading Zone
Amazon Store (with international branches)
Yahoo Auctions (with international branches)

The Software Collectors Mailing List
MobyGames
The Legacy
Stephen Emond's Collectors Guide
Jocksitter's Collection
KtJ Dragon's Japanese Ultimas
Tom Mage
The Origin Museum
The Collectible Ultima
The Computer and Book RPG/Adventure Museum
Ye Old Infocom Shoppe
Vintage Sierra
Synchronic Web

Mysterious Sosaria
Pentagram - Ultima VIII Engine
Exult - Ultima VII Engine
Nuvie - Ultima VI Engine
Ultima III Recreation Project
Iris - the *real* 3D client for Ultima Online
Ultima IV - Virtue of Humility
xu4 - Ultima IV Remake