Al Lowe's Humor Site - Though not strictly about his games, funnyman Al's site is great for a break.
The Infocom Fact Sheet - Very detailed information on Infocom's individual products.
The Infocom Gallery - Great visuals of Infocom games.
The Interactive Fiction Collector's Guide - A good resource for those interested in collecting interactive fiction, especially for those interested in companies outside of Infocom (although Infocom is included).
The Magnetic Scrolls Memorial - A grand tribute to the British version of Infocom.
Moby Games - Massive encyclopedia of both old and new games.
The Notable Ultima - Extremely detailed site includes chronologies, trivia, and transcripts. Of particular note is the "The Collectible Ultima" section, which discusses the games from a collecting viewpoint.
The Origin Museum - A collector site devoted to Origin's games (not just Ultima). Especially detailed information on the Wing Commander series. Pictures of unusual items such as the Ultima Crossbow.
Scott Adams Grand Adventures (SAGA) - Official website of Scott Adams, founder of Adventure International, still alive and gaming.
Tom (Mage)’s Ultima and Infocom Page - Give Tom a holler to find out just about anything about Ultima.
Ultima Collector's Guide - Site describes the Ultima series strictly for collecting purposes. Tells the contents of the various packages and delves into package variations. Small pictures of the packaging and some contents included.
The Underdogs - Large game database. Concentrates on underrated games. Great place to find info on little-known games.
Vintage Sierra - Pictures, descriptions, forum discussions, and articles about the prolific Sierra line of games.
Ye Olde Infocomme Shoppe - Emporium of collector games for sale or trade. Plus articles on the collecting hobby, pictures of rare items, and more.