The Labyrinth" (old version, new version) 

Excellent site that contains links to a wide range of medieval resources; a new version is under construction.  Currently, it contains the following categories:

The Labyrinth Library

• "Auctores et fontes" (primary texts, some translated, some in the original language)
• "Scripta moderna" (secondary texts)

National cultures

• Anglo-Saxon
• Byzantium
• Celtic
• England 1066-1500
• France
• Germany
• Iberia
• Italy
• Scandinavian Cultures

International culture

• Archaeology and Cartography
• Arts and Architecture
• Medieval History
• Latin
• Paleography and Codicology
• Music
• Philosophy and Theology
• Social History
• Religious History
• Sciences

Special topics

• Arthurian Studies
• Crusades
• Heraldry
• Arms
• Chivalry
• In the Margins: Medievalism in Postmodern Contexts
• Labyrinths
• Medieval Women
• Vikings, Runes, and Norse Culture

Miscellaneous

• Pedagogical resources
• Professional information, publications, and organizations
• Labyrinth electronic center
• Medieval studies text, image, and archival databases

NetSERF (old address, new address)

Wonderful site that currently maintains over 950 links to medieval studies sites, organized by subject.  You'll find information in the following categories:

• Archaeology
• Architecture
• Art
• Civilizations
• Culture
• Drama
• History
• Law
• Literature
• Music
• People
• Philosophy
• Religion
• Science and Technology
• Women

There is also a "research center," which features the following: 

• Archives and Libraries
• Articles and Papers
• Associations
• Organizations and Societies
• Bibliographies
• Conferences and Seminars
• Degree Programs
• Financial Aid
• Journals
• Mailing Lists and Newsgroups
• Maps
• Museums
• Other Internet Indicies
• Teaching Material and Syllabi

ORB

The medieval "Online Reference Book" contains vast amounts of useful information.  Unlike the other resources mentioned above, it consists not primarily of links to other sites, but rather of a collection of texts.  ORB has three major components: the Encyclopedia; the Textbook Library; and the Reference Shelf.

The Encyclopedia 

This is "a  chronological and geographical index of essays, bibliographies, images, documents, links, and other resources." It covers the following:

• European history from the collapsing Roman empire to the late Middle Ages
• Religion
• Culture, which includes:
• Art and architecture
• Books and universities
• Law
• Literature
• Magic and witchcraft
• Music
• Philosophy
• Science and technology
• Urban studies
• Women's studies

The Textbook Library

This has "full-length textbooks, written by experienced scholar-teachers." Topics include:

• Paleography
• Old English
• Lectures for a medieval survey
• Western civ.
• A history of medieval England
• A short course on the medieval church
• Celtic art and cultures
• The crusades

The Reference Shelf

This contains "links to excerpts and full texts from primary and secondary sources, housed at the ORB server or elsewhere on the World Wide Web."  Includes not only links to primary texts on the web, but also the massive Internet Medieval Sourcebook, a collection of primary texts focusing primarily on history, law, and saints' lives, as well as guides to medieval music and medieval-themed films).  

There are also Resources for Teaching, a section on General Interest, and External Links (worth consulting mainly for French medieval literature)

"The Voice of the Shuttle"

Huge collection of links for the humanities, with entries on topics ranging from "Anthropology" to "Women's Studies."  The category "Literature (English)" is organized by period: Medieval, Renaissance, Restoration, Romantics, Victorian, etc.  

If you follow the "Medieval" link, you fill find the following entries: 

• General resources
• Authors, works, projects
• Course syllabi and teaching resources
• Criticism and critics
• Journals
• Listservs and newsgroups
• Reference works
• Conferences and calls for papers
• Medieval studies programs, centers, and associations
• Fonts for display of Old English

Mediaevum.de

For those who read German, this is an excellent meta-page that contains the links to the following: 

Addresses and Homepages

• Departments
• Institutions of Research
• Libraries
• Archives
• Scholarships & Grants
• Publishing Companies

Medieval Studies

• Current Projects & Research Work
• Recent Publications
• Conference Calendar
• Mailinglists & Internet Periodicals

Bibliographical Information

• Databases
• OPACs
• Searching for Manuscripts

Sources of Information and Tools

• Text Programs
• Fonts for Medieval German Texts
• Databases
• Dictionaries
• Medieval Calendar

German and Latin Texts on the WWW

Manuscripts on the Net

• Databases for Research
• Facsimiles
• Images

Related Fields of Research

• Theology
• Philosophy
• Art
• History
• Curio Gallery

Search Engines

Google.com