Learning really IS fun!
General
Enchanted Learning
Language Arts
Spelling - Alpha-bot
Vocabulary - BIGbot
Jumbles - Jumble Kids
Picture Dictionary - Little Explorers
Social Studies
Colonial Williamsburg Living Museum
Science
More Science Sites below:
The Franklin Institute Science Museum
NASA Kids' Club
BrainPop - A free animated movie, featuring Moby the Robot and Tim discussing various topics.
StudyJams - math and science sites with music, videos, slideshows, and tests.
DK Find Out! - Interactive Online Encyclopedia for Kids
NOAA - Fun for Kids
Math