History Channel's Holocaust Site - provides facts, photo galleries, and a video interview of an allied veteran who witnessed the concentration camps during liberation.
Holocaust Encyclopedia - provides articles, photos of artifacts, documents, films, id cards, maps, photos, and songs that document the Holocaust.
JewishGen's Holocaust Database - is a collection of databases containing information about Holocaust victims and survivors.
Jewish Virtual Library - a comprehensive site that provides basic history, reference maps, and information on the Nazi party, concentration camps and persecution, rescuers, resistance fighters, victims, the world reaction, and the aftermath of the Holocaust.
United States Holocaust Memorial Museum - a great site where with information about the Holocaust, survivors and victims, and preventing genocide and anti-semitism. The site also provides the Holocaust Encyclopedia linked above, resources for educators, and exhibit information for those interested in visiting the museum in Washington, DC.
Voices of the Holocaust - provides survivor testimonies, background information on the Holocaust, maps, statistics, and Nazi policies. The site is provided by the British Library.
Yad Vashem The World Holocaust Remembrance Center - is the ultimate source for Holocaust education, documentation, commemoration and research. The site provides several digital collections including a name database, photo archive, documents archive, and online film catalog.