Holocaust Encyclopedia (USHMM)
Interactive Timeline of Events (USHMM)
Printable Timeline of Events (USHMM)
36 Questions (link to the Simon Wiesenthal Center's Museum of Tolerance)
Glossary (link to the USHMM)
Statistics - Jewish Populations and Losses by Country (pdf)
Tell Them We Remember: the Story of the Holocaust, by Susan D. Bachrach. A Holocaust overview geared toward students.
The World Must Know: the History of the Holocaust As Told in the United States Holocaust Memorial Museum, by Michael Berenbaum. A comprehensive Holocaust primer.