Citation Styles:

• Purdue Owl  APA, MLA, and Chicago style format guides.

 Literature:

• Library of Congress
• Britannica

General:

• Khan Academy
• WolframAlpha

Algebra:

• Khan Academy (Algebra 1)
• Khan Academy (Algebra 2)

Geometry:

• Khan Academy (Geometry)

Calculus:

• Khan Academy (Pre-Calculus)
• Khan Academy (Calculus)

World History:

• Archives
• Crash Course (World History 1)
• Crash Course (World History 2)
• History of the World (BBC)
• National Geographic

U.S. History:

• Crash Course
• Library of Congress
• National Parks
• Smithsonian
• United States History

General:

• Crash Course
• Everyday Mysteries
• Google Earth
• How Stuff Works
• National Geographic
• Periodic Table
• USGS

Astronomy:

• Astrogeology (USGS)
• NASA
• Solar System (Britannica)
• Solar System (National Geographic)
• Space Place (NASA)

Biology:

• Britannica
• Evolution
• Genetics
• Kingdoms Of Life
• Natural Selection
• Science Daily

Chemistry:

• American Chemistry Society
• eChemPortal
• History of Chemicals
• Khan Academy (Chemistry)
• Visual Elements Period Table
• WolframAlpha (Chemistry)

Earth Science:

• Geological Society of America
• National Ocean Services
• National Science Foundation
• Ocean (Smithsonian)
• Plate Tectonics (The Geological Society)

Ecology and Conservation:

• Conservation (USDA)
• The Conservation Fund
• Ecology (DATA)
• Ecology (USGS)
• National Parks

Geology:

• 8 of the World's Most Dangerous Volcanoes, According to Experts (Time)
• Earthquake
• Earthquake Risk (FEMA
• Erosion (National Geographic)
• Geology (USGS)
• The U.S. Volcanoes and Current Activity (USGS)

Meteorology:

• Meteorology (ScienceDaily)
• National Weather Service
• Ozone (NASA)

Physics:

• American Physics Society
• Physics (APS)
• Physics World