The World Book Online- In addition to the expected 25,000-plus encyclopedia articles, provides tables, animation, illustrations, maps, audio clips, timelines, a dictionary, current events, and more.

CQ Researcher
Explore all sides of current issues in depth

Bartleby
http://www.bartleby.com/reference
Links to many standard, classic reference tools

Fifty States
http://www.50states.com/fileindx.htm
Facts about all fifty states, including state birds, flowers, songs, etc.

General Reference Center Gold - A general interest database to find articles from newspapers, reference books, and periodicals, many with full-text and images. Find the latest current events, popular culture, business and industry coverage, the arts and sciences, sports, hobbies, and more.

GreenFILE

Relationship of humans and the environment, including global warming, recycling, alternative fuel sources, and more. Scholarly and general interest titles, as well as government documents and reports, including some full-text material.

Science Online-Overview of the sciences based on the National Science Education Standards curriculum. Diagrams, definitions, timelines, biographies and essays are arranged by discipline and are thematically connected with hyperlinks.  Experiments - once a separate database - are included, grouped into broad subject catgories such as biology, physics, space, earth science, etc.