Entertainment Resources:

Internet Movie Database
The Leaky Cauldron
Backstage West
Hollywood Reporter
PBS
A&E
BBC
YouTube

Mathematics:

Roman Numerals 
Math Forum 
Math Page
MIT World Web Math
Finite Mathematics and Calculus
Algebra
Calculus on the Web
Math Reference Tables
Planet Math

Internet Resources:

Webopedia
Alta Vista
Ebig.com
About.com
Google
Excite.com
Northern Light
IT Encyclopedia

General Information:

Wikipedia
Encarta
Library of Congress
The World Factbook
Photo Vault
MIT Open Courseware
How Stuff Works

Social Science

Spartacus Educational (history)
World Embassies
Nolo(US law)
Congressional Districts
U.S. Senate (members)
U.S. Congress (members)

Travel:

Time Zones
Currency Converter
Wizard Currency Conversions
Mapquest
Metric Conversions
White Pages

Medicine and Health:

NHS Direct
EMedicine
Mayo Clinic  
First Aid
Web MD
Myozen
Virtual Hospital
Anatomical Dictionary

Science:

Beakman and Jax (science made simple)
Scientific American
"Ask the Experts"
Periodic Table
Physics
"Optics and Microscopics"
Astronomy Cafe

Language Arts:

Merriam-Webster Dictionary
Cambridge Dictionary
World Wide Words
Wordsmith.org (word of the day)
Double Tongued Dictionary
Urban Dictionary
British-American Slang
British Terms
Focal an Lae (Irish phrases)
Babel Translations
Elvish
Acronym Search
Spanish Radio
Learn Spanish

News Media and Information:

New York Times
The Boston Globe
The Washington Times
Detroit Times
Snopes (urban legends dispelled)
Chronicle of Higher Education
CNN
NPR

Books and Literature:

Bartleby.com (literature, verse)
Questia (on-line library--free previews)
Book Crossing

Social Reform:

ACLU
Amnesty International
MLK Papers
PETA
Child Support Enforcement
Znet
Public Citizen
The Wilderness Society
Oxfam America
National Organization for Women

Directories:

Web Radio Directory
White Pages