Ultima IV Website, by Samson Dragon

Provides walkthroughs, maps, and utilities.
http://www.fortunecity.com/rivendell/dark/169/

Ultima IV Solution

Bare-bones walkthrough including all essential steps and items, by Stephen Lee.
http://members.aol.com/UltimaFile/files/u4.txt

Ultima IV: Gaining Virtue

List of actions that alter your virtue in the game.
http://martin.brenner.de/ultima/virtuechanges.html

GameFAQs: Ultima IV

FAQs, walkthroughs and town script.
http://www.gamefaqs.com/computer/doswin/game/11099.html

Ultima IV: Quest of the Avatar

Origin's official site. World and dungeon maps, walkthough, documentation, and music files.
http://www.uo.com/archive/ultima4/

Ultima Personality Test

Virtue based class-determination questions, game crib sheet, and character files.
http://www.tk421.net/ultima/

Optima IV

A Virtual Basic clone of Ultima III and IV. With game design information, screenshots and download. Source and additional modules are available.
http://www.wizardportal.com/optimaiv/

Ultima IV: The Dawn of Virtue

A fan remake project with 3D rendered isometric graphics.
http://www.hut.fi/~jtpelto2/ultima4/

xu4 - Ultima IV Recreated

A remake of the classic computer game Ultima IV for modern operating systems.
http://xu4.sourceforge.net/