Best of History Websites:
A quick, convenient, and reliable access to the best history-oriented resources online in a wide range of categories. 
Source: Best History Sites

Digital History: 
Explore American History through multimedia and interactive content.
Source: Digital History

EyeWitness to History: 
History through the eyes of those who lived it.
Source: Eye Witness History

Have Fun With History: 
Free videos & activities for  lovers of American History.
Source: Have Fun with History

History Matters:
A guide to the most useful websites for teaching U.S. History and Social Studies.
Source: History Matters

iCivics:

iCivics teaches students how government works by having them experience it directly through their games.

Source: iCivics

American Museum of Natural History: 
Knowledge about human cultures, the natural world, and the universe.
Source: AMNH

First World War:
A multimedia history of World War I.