Bundesarchiv Internet

German Historical Archive - For students and academics studying German history, this (http://www.bundesarchiv.de) is the key site for access to all publicly available German state archives. There are inevitable gaps – huge volumes of historical documents were destroyed by allied bombing and shelling during the Second World War. Interestingly, relatively few documents were destroyed by the Germans themselves – possibly national stereotypes of 'wanting order' may not be wholly inaccurate?
The English language section of the state archive can be found at http://www.bundesarchiv.de/index.html.en
The main sections are divided into 8 historical periods:
• Federal Republic of Germany (from 1949)
• German Democratic Republic (1949-1990)
• Allied Occupation Zones (1945-1949)
• German Reich: National Socialism (1933-1945)
• German Reich: Weimar Republic (1918-1933)
• German Reich: Kaiserreich (1871-1918) including North German Confederation (1867-1871)
• German Confederation (1815-1866) and Provisional Central Power (1848/49)
• Holy Roman Empire (1495-1806)

The area of most interest to the majority of modern history students is the rise of fascism and the Second World War.
Investigation of National Socialist (Nazi) Crimes
The Records of the Central Office of the Judicial Authorities of the Federal States for the Investigation of National Socialist Crimes in Ludwigsburg

Investigation of National Socialist (Nazi) Crimes
The Records of the Central Office of the Judicial Authorities of the Federal States for the Investigation of National Socialist Crimes in Ludwigsburg - Short Introduction into Records and Terms of Use

Library holdings on the military
Bibliotheksbestand zum Militär
Conventional library catalogues
Konventionelle Kataloge
Research on the Nazi era
Research on persons in the holdings on the Nazi era generally only yield good results in certain cases.
"Euthanasia" in the Third Reich
An unpublished private letter from Hitler, backdated to 1 September 1939, instigated the German Reich's secret programme of mass murder of people with mental illnesses or disabilities, which cost the lives of more than 200,000 patients by 1945.
NS archives of the Ministry for State Security
The so-called NS (Nazi) archives of the Ministry of State Security arrived in the custody of the Central State Archives of the GDR after the disbandment of the Ministry of State Security (MfS) in 1990.
Documentation on the persecution of Jews
Since the start of the 1960s, the Federal Archive has been working to document the names of those Jewish citizens who were sent to their deaths or deported as a result of persecution in Nazi Germany.

There are links to personal papers, maps, official documents, film, publications, technical designs, etc., etc. A huge amount of information.
For whatever period of German history interests you, there will be something worth looking at on this website.