Professional societies:

American Philological Association

Modern Language Association

American Association for Neo-Latin Studies

Medieval Academy of America

Medieval studies conferences:

Annual Meeting of the American Philological Association (host of MLSG panels)

Kalamazoo International Congress on Medieval Studies

University of Leeds International Medieval Congress

International Congress for Medieval Latin Studies

Annual Meeting of the Medieval Academy of America

Vagantes

Useful resources on the web:

The Internet Medieval Sourcebook

Monumenta Germaniae Historica online

Perseus Project

The patristic library in English

Online text of the Latin Vulgate Bible

Texts of classical and late classical authors

The Latin Library (many medieval Latin texts)

Mediaevum's medieval Latin texts

Dictionary of Latin place names

The Labyrinth