Jewish Encyclopedia (1906): This is a historical work from the early 20th century that has not been updated.  

YIVO Encyclopedia of Jews in Eastern Europe: A definitive work about the civilization of Eastern European Jewry; includes primary source materials such as documents, images, audio and video, as well as maps. A print edition is available here.

Jewish Women: A Comprehensive Historical Encyclopedia: Edited by Alice and Moshe Shalvi, made available online by the Jewish Women's Archive.

Encyclopedia of Jewish Folklore and Traditions (2012): Covers beliefs and practices, holidays, artifacts, Jewish ethnographers, and surveys countries. 

Encyclopedia of the Bible and its Reception (EBR): A comprehensive guide to the current state of knowledge on the background, origins, and development of the canonical texts of the Bible as they were accepted in Judaism and Christianity. Covers literature, visual art, music, film, and dance, as well as the reception of the bible in Islam and other religious traditions and new religious movements.

Encyclopedia of the Dead Sea Scrolls: Edited by Lawrence Schiffman and James VanderKam, this Oxford Press encyclopedia features 450 articles about the history and meaning of the Dead Sea scrolls, and descibes the controversies that surround them.

Yad va-Shem Holocaust Lexicon: Entries are based on Yad ve-Shem's Encyclopedia of the Holocaust.

Biographies

The Concise Dictionary of American Jewish Biography (1994): Edited by Jacob Rader Marcus and Judith M. Daniels, made available online by the American Jewish Archive.

Jewish Women Archive: A comprehensive online database; includes encyclopedia, bibliogrpahies, and specific collections such as the Femisit Revolution. 

Fifty Key Jewish Thinkers (1997): Electronic reproduction of the 1997 edition; The 2007 second edition is available in print.

Other Suggested Resources

Stanford Encyclopedia of Philosophy: Each entry in this dynamic reference work is authored and updated by an expert or group of experts in their field; maintained by Stanford University.

• Academic Jewish Studies Internet Directory

• Academic Guide to Jewish History

• All about Jewish Theater: Iincludes commercial information, book reviews, call for papers and information on upcoming conferences and festivals.
• Berman Jewish Policy Archive: A central electronic repository for Jewish communal policy sources.
• International Institute for Jewish Genealogy
• Programs in Jewish Studies: Association of Jewish Studies.
• Sephardi Mizrahi Studies: "Promotes the integration of academic Sephardi and Mizrahi Studies into general Jewish Studies and other fields outside of Judaic Studies".

General

Encyclopedia of Jews in the Islamic World. Norman A. Stillman; editors, Phillip I. Ackerman-Lieberman ... [et al.]. Leiden ; Boston : Brill, 2010.

The YIVO Encyclopedia of Jews in Eastern Europe. Gershon David Hundert, editor in chief.  New Haven [Conn.]: Yale University Press, 2008.

The Cambridge Guide to Jewish History, Religion, and Culture. Judith R. Baskin and Kenneth Seeskin (Eds.). Cambridge; New York: Cambridge University Press, 2010: A comprehensive overview of Jewish life, from its origins in the ancient Near East to its impact on contemporary popular culture.

Encyclopedia of Hebrew Language and Linguistics: Khan, Geoffrey, and Shmuel Bolozky. 2013. Leiden [etc.]: Brill. A comprehensive, first of its kind porject in 4 volumes.

Specific Topics

The Oxford handbook of Judaism and economics. Aaron Levine, editor. Oxford University Press, 2010

Cambridge Histories Online:

• The Cambridge History of Jewish Philosophy Vol. 1. From Antiquity through the Seventeenth Century
• The Cambridge History of Judaism, 4 Volumes.

Holocaust Studies

The Encyclopdia of the Holocaust. Israel Gutman, editor in chief. New York: Macmillan, 1990.

The Encyclopedia of Jewish Life before and during the Holocaust. Editor in chief, Shmuel Spector ; consulting editor, Geoffrey Wigoder; foreword by Elie Wiesel.  Jerusalem: Yad Vashem; New York : New York University Press, 2001.

The Holocaust Encyclopedia. Walter Laqueur, editor; Judith Tydor Baumel, associate editor. New Haven: Yale University Press, 2001.

Encyclopedia of Holocaust Literature. Edited by David Patterson, Alan L. Berger, and Sarita Cargas. Westport, Conn.; London: Oryx Press, 2002.

Holocaust Literature: an Encyclopedia of Writers and their Work. S. Lillian Kremer, editor. New York: Routledge, 2003.

Holocaust Survivors: a Biographical Dictionary. Emily Taitz. Westport, Conn.: Greenwood Press, 2007

The Oxford Handbook of Holocaust Studies. Edited by Peter Hayes and John K. Roth. New York: Oxford University Press, 2010.

The Routledge Atlas of the Holocaust. Martin Gilbert. London; New York: Routledge, 2002.

Biographies

Jewish autobiographies and biographies: an international bibliography of books and dissertations in English: David Zubatsky, 1989.

Biography Index Retrospective: 1946-1983: Provides information about people from antiquity to 1983, from resources from from 1946 to 1983, in a single, easy-to-use database. Research people in the headlines or throughout history; find information on notables across all disciplines and subject areas with this practical resource.

Biography and Genealogy Master Index: Indexes current reference sources & the retrospective works that cover individuals, both living & deceased, worldwide. Covers biographical dictionaries; who's whos; subject encyclopedias with biographical entries; literary criticism; & other sources.

Calendars

Hebrew Date Converter: Convert a Gregorian calendar date into the equivalent date on the Hebrew calendar, and vice verse. Includes Hebrew view.

Jewish Holidays Calendar, 1998-2017.

Directories

Hasidic Rabbis listing (Hebrew)

Jewish.net: A general Jewish directory.

Olam ha-Torah: A directory of Jewish benevolent institutions.