GENERAL HELP:
http://www.shmoop.com/ - Shmoop offers synopses on a variety of subjects ranging from Pre-Algebra to Literature and History. They also offer fee-based test prep programs.

ENGLISH & LITERATURE:
http://www.sparknotes.com/ - Sparknotes has summaries and analysis of almost all books commonly read in school. Before using sparknotes, you need to have read the text.

http://absoluteshakespeare.com/ - Absolute Shakespeare has both the full text and summaries of all the collected works of Shakespeare. As with sparknotes, it is more helpfull if you have read the full text before utilizing the summaries.

http://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style - The Wikipedia Manual of Style, though written primarily for Wikipedia's editors, is an engaging and complete overview of grammar.

HISTORY:
http://historyteacher.net/ - One of the best history resources on the internet, this is actually the basis of at least one Broughton history teacher's class

SCIENCE:
http://en.wikipedia.ord/wiki/Periodic_Table_(large_version) - Never work on or tutor someone in chemestry without a large copy of the periodic table.

http://www.smuhsd.k12.ca.us/bhs/science-dept/marcan/references.html - A detailed set of notes and reference formulae for the Zumdahl Chemistry Book (AP Chemistry).

http://www.apphysicslectures.com - More than 200 videos explaining physics.

http://www.sparknotes.com/biology/, http://www.sparknotes.com/chemistry, http://www.sparknotes.com/physics/ - Sparknotes also has great science resources.

FOREIGN LANGUAGE: We will have more helpful links for other languages for you as we find them, thank you for your patience.

http://www.studyspanish.com/ -- Studyspanish.com has a lot of free quizzes and worksheets and lessons for all of the grammar

http://www.my-spanish-dictionary.com/ -- My Spanish Dictionary is an excellent resource for anyone who's interested in learning more about Spanish and its heritage.

MATHEMATICS:
http://shodor.org/interactivate/ - Shodor's Interactivate has a wide variety of games and discussions about various mathematics topics.

http://www.math.com/ - Math.com has concise summaries of all of the basic math classes that could be taken in high school.

http://en.wikipedia.org/wikipedia/Main_Page - Wikipedia has excellent overviews of many math topics, although some discussions may go far beyond the highschool level.