• Bibliographischer Werkzeugkasten
  A large collection of Internet reference sources, compiled by German librarians.
• Deutsche Internetbibliothek
  Collection of useful reference links compiled by German public libraries.
  
• SwissInfoDesk
  Links collected by the Swiss National Library.
  
• wissen.de
  A "knowledge portal" offering free search of Wahrig dictionaries. In addition, time tables of history and assorted information ranging from gardening tips to pets and recycling, etc..
• Xipolis
  Allows searching of Duden, Brockhaus, Kindlers Literaturlexikon, etc. Full text of entries is fee based (restricted to participating libraries).
  
  

Dictionaries and Encyclopedias

Language Dictionaries

• Adelung Wörterbuch
  All four volumes of this 1811 dictionary are available full-text.
• FreeDic
  Excellent English-German/German-English Dictionary
• Collins English German/ German English Dictionary
  
• LEO German-English Dictionary
  Claims to contain over 300,000 terms.
  
• Middle High German dictionaries
  Free access to the two standard dictionaries of the Middle High German language, "Lexer" and "Benecke/Müller/Zarncke".
• Phrasen.com
  English-German idiomatics.
  
• woerterbuch.info
  German-English dictionary
  
• Wortschatz Lexikon
  
An interesting project of the Abteilung Automatische Sprachverarbeitung at the university in Leipzig. More of a corpus search engine than a dictionary proper.

Encyclopedias

• Biographisch-Bibliographisches Kirchenlexikon
  
• Österreich-Lexikon
  
• Wikipedia
  This is the German version of the Wikipedia
• Zedler Universallexikon
  Major 18th century German encyclopedia.

General Country Information, Tourism.

• CIA World Factbook
  Consult the country listing for detailed information about all German-speaking countries.
• General Information about Austria
  (from the Austrian Press and Information Service)
• German Information Center
  Information about Germany from the German Embassy in Washington, DC..
• Servus in Österreich
  
• SwissInfo and SwissInfo Toplinks
  

German Zip Codes etc.

• Postleitzahlen-Auskunft
• Area Codes
  
  

• Bahnen und Busse
  Train and bus schedules (Germany and Europe)
  
• Deutsche Bahn AG Fahrplanauskunft
  Official train schedules for Germany
• Swiss train schedule

Maps

• Austria
• Germany
• Liechtenstein
• Luxemburg
• Switzerland

These maps are more detailed than the small CIA maps in the World Factbook. Also from the University of Texas, some historical maps of Europe.