Sierra's Resource Files
Here are various links to some interesting graphics, audio and text I've found in the resource files of Sierra's various VGA/SVGA adventure games using SCI Viewer. There are a lot of images on these pages, so proceed cautiously if you're using dial-up. There's also a slight spoiler risk on some of the pages. (Note: SCI Viewer's homepage was hosted on Geocities, so their page is down at the moment. You can still download SCI Viewer from my site, however.)
UPDATE 5-5-12: Now that I have the Roberta Williams Collection, I have access to the resource files of Phantasmagoria. However, I just now got around to adding various art and animations to that game's section on the Miscellaneous page, and I added so much material that decided to give Phantasmagoria a page of its own.
UPDATE 11-15-13: The Space Quest entries have been moved from the Miscellaneous section to a page of their own. Additionally, info on the SQ4 beta has been added to the SQ5 beta's page.
King's Quest 7
Leisure Suit Larry 7
Miscellaneous (King's Quest 5 and 6; Freddy Pharkas, Frontier Pharmacist; Gabriel Knight 1; The Bizarre Adventures of Woodruff and the Schnibble)
Quest for Glory Series
Inside the Chest/Behind the Developers' Shield (King's Quest)
The Space Quest Series
BONUS - Exploring the Beta Versions of SQ4 and SQ5
Hidden Items from other Companies' Games
The Discworld Easter Egg Conundrum - NOW (almost) SOLVED!!
Legend of Kyrandia (added 12-4-12!)
See many, many more Sierra (and LucasArts) oddities at ATMachine's House of LucasArts and Sierra Oddities.