Amblesideonline.org is a Charlotte Mason-style program that has art, nature study, history, literature and more for every grade using many free online living books.
Mathfactcafe.com lets you generate math worksheets, drills and flashcards for elementary school children.
MSNucleus.org offers a free science curriculum for all grades, and Eequalsmcq.com offers a free life science curriculum for elementary-aged children.
Starfall.com teaches kids to read with fun stories, games and other activities.
Meet the Masters is a free art-appreciation course for those in kindergarten to the fifth grade, with study questions and activities.
Bbc.co.uk offers free foreign language course for learning French, German, Spanish, Greek, Chinese and other languages. Fsi-language-courses.com offers free courses developed by the Foreign Service Institute in a multitude of languages.