Quick reference 

• Abbreviations.com If there is an abbreviation you need, you'll find it here.
• AMDOCS  "Documents for the study of American History"
• Artcyclopedia: the Fine Art Search Engine John Malyon, Artcyclopedia, Inc.
• Background Notes  United States Department of State Background Notes include facts about the land, people, history, government, political conditions, economy, and foreign relations of independent states, some dependencies, and areas of special sovereignty.
• Bartleby.com  Great Books "The preeminent Internet publisher of literature, reference and verse providing students and researchers and the intellectually curious with unlimited access to books and information on the Web, free of charge."
• BJ Pinchback's Homework Helper "Someone has done a lot of research and linked together some great Web sites." -- The Teaching Home Magazine
• Brain Pop  "... animated, curricular content." Multiple topics. Very cool.
• College Board Helpful hints and information for taking tests and getting into college.
• Digital Public Library of America Explore 8,007,019 items from libraries, archives, and museums. Includes photos, music, video.
• Goodreads  "...world's largest site for ... book recommendations"
• Infoplease Homework helper.
• Infoplease,  Homework Center - Grammar and Spelling Guide  "... a grammar and style guide, detailed descriptions of the parts of speech and their uses, suggestions for writing better and stronger sentences and tips to help make you a better speller."
• Khan Academy  "... extensive video library, interactive challenges, and assessments from any computer with access to the web. Complete custom self-paced learning tool..."
• The Online Books Page "...more than a million works in various formats... free for personal, noncommercial use."
• Refdesk.com "Fact checker for the Internet."  Great links.
• USHistory.org Free high-school courses for students, teachers, home-schoolers, and history lovers.