There are numerous genealogical and historical resources and databases online for genealogists researching their Jewish ancestors. Most of these Jewish genealogy databases are even free!
Yad Vashem and its partners have collected the names and biographical details of more than three million Jews murdered by the Nazis during World War Two. This free database includes information taken from a variety of sources, including my favorite - pages of testimony sent in by Holocaust descendants. Some of these date back to the 1950s and include parents' names and even photos.
Search data on more than four million people, from family trees submitted by more than 3,700 Jewish genealogists worldwide. Free from JewishGen, the International Association of Jewish Genealogical Societies (IAJGS) and the Nahum Goldmann Museum of the Jewish Diaspora (Beit Hatefutsot).
Search for free in this online compilation of surnames and towns currently being researched by over 80,000 Jewish genealogists worldwide. The JewishGen Family Finder database contains over 400,000 entries: 100,000 ancestral surnames and 18,000 town names, and is indexed and cross-referenced by both surname and town name.
While the majority of Ancestry.com's historical databases are only available to paid subscribers, many of the Jewish Family History Collections will remain free as long as they exist on Ancestry.com. Partnerships with JewishGen, the American Jewish Joint Distribution Committee (JDC), the American Jewish Historical Society and the Miriam Weiner Routes to Roots Foundation, Inc. have created a large online collection of free Jewish historical records, including census and voter lists, vital records and more. Free and subscription records are mixed in these collections, so beware - not everything is open to non-subscribers!
Avotaynu, the journal of Jewish genealogy, hosts the free Consolidated Jewish Surname Index (CJSI), a gateway to information about 699,084 surnames, mostly Jewish, that appear in 42 different databases which combined contain more than 7.3 million records. Some of the databases are immediately accessible on the Internet, while others are found in published books and microfiche, available from most Jewish genealogical societies around the world.
This free searchable database on JewishGen includes names and other identifying information from cemeteries and burial records worldwide.
This free Internet site serves as a digital monument dedicated to preserving the memory of all the men, women and children who were persecuted as Jews during the Nazi occupation of the Netherlands and did not survive the Shoah - including both the native-born Dutch, as well as the Jews who fled Germany and other countries for the Netherlands. Each individual has a separate page commemorating his or her life, with basic details such as birth and death. When possible, it also contains a reconstruction of family relationships, as well as addresses from 1941 or 1942, so you can take a virtual walk through streets and towns and meet their neighbors as well.
Free online database allows you to search by town or country to determine what Jewish and other records are held by archives for Belarus, Poland, Ukraine, Lithuania, and Moldova. The archives indexed on the Routes to Routes site include the Lviv Historical Archive, Krakow Archives, Przemysl Archives, Rzeszow Archives, Tarnow Archives, and Warsaw AGAD Archives, plus regional archives in Lviv, Ivano-Frankivsk (Stanislawow), Tarnopol, and others. These records are not online, but you can print out a list for your ancestor's town which will tell you what records are available and where/how to access them.
If you have ancestors who perished or fled from various pogroms or the Holocaust, a great deal of Jewish history and memorial information can often be found in Yizkor Books, or memorial books. This free JewishGen database allows you to search by town or region to find descriptions of available Yizkor books for that location, along with the names of libraries with those books, and links to online translations (if available).
The Knowles Collection, a free popular database of Jewish records hailing from the British Isles, builds upon work commenced by the lage Isobel Mordy - a well-known historian of the Jews of the British Isles. Todd Knowles has greatly expanded this collection to over 40,000 names from over 100 individual sources. Available free online at FamilySearch.org in Gedcom format that can be read by your genealogy software, or by the free online PAF genealogy software available for download on the same page.