Databases:

• General OneFile  A one-stop source for news and periodical articles on a wide range of topics.

• General Reference Center Gold  Provides one-stop access to general interest magazines, business
  periodicals, reference books, maps, historical images, and newspaper articles.

Language:

• Acronym Finder

• AlphaDictionary Site

• ARTFL Project: American and French Research on the Treasury of the French Language

• Bartleby.com Reference (Encyclopedia, Dictionary, Thesauri, Quotations, English Usage, Etc.)

• Bartlett's Familiar Quotations (10th ed, 1919)

• iTools (Dictionaries and Such)

• Merriam-Webster Dictionary and Thesaurus

• OneLook Dictionaries

• Style Manuals & Writing Guides

• Word Oddities and Trivia

• WordNet: a Lexical Database of the English Language

Maps and Geography:

• Country Studies:  The Country Studies Series presents a description and analysis of the historical setting and the social, economic, political, and national security systems and institutions of countries throughout the world. 
• Google Maps 

• Great Lakes Information Network - Detailed maps of the Great Lakes. 

• Library of Congress Map Collections: 1500-2003 

• MapQuest - U.S. street maps and driving directions. 

• Sun and Moon Data - Times of sun and moon rising, setting, transit, and moon phase for any day at any location on the globe.

• Topozone - Easy to use interactive online topographical map of the entire United States. Maps are derived from USGS maps.

Statistics:

• Fed Stats - Links to statsitics from more than 100 federal agencies.

• Statistical Abstract of the United States

Units of Measure:

• Calculators On-Line Center

• Consumer Price Index

• Currencies of the World

• Measuring Worth.com (Inflation, Purchasing Power of the Dollar, etc.

• megaConverter

• Online Conversion - Convert Anything to Anything Else

• PollingReport.com

• Price's List of Lists (Rankings, Fortune 500, etc.)

• Time (Official U. S. Time)

• Unit Conversion

• What Is a Dollar Worth?