Free (applies to items that often cost money)
Explaining the "God particle" to a seven-year-old

Business articles from Wharton Business School for high school students

The 39 Clues

Scratch

Fundamentals of Chinese Characters -- Free sample content from the book

learning Chinese -- free Chinese Character Writing Exercise Sheets

print Chinese flash cards for free -- yellowbridge.com

Globulation -- an online real-time strategy game

word list generator -- for decodable texts

68 decodable fiction passages from free-reading.net -- second grade level

68 decodable fiction passages from free-reading.net -- first grade level

free-reading.net -- free decodable texts

MIT-sponsored free science summer camp for high school juniors and seniors (RSI)

Take University of California, Berkeley courses online for free

Alice programming (sample test at the end of an Alice course)

Alice in Action book -- free code examples

free online translator

PhDIQtest.com -- free IQ test

hotchalk.com -- free classroom management software (web-based)

Online games at happystar.com.cn

Use Google to search in other languages!

createspace.com -- publish your own book with Amazon

publishamerica.com -- publish your own book

biguniverse.com -- read hundreds of children's books online for free

Free reading games for beginning readers from readingsparkers.com

Teaching Java to kids -- a list of resources

Teaching Java to kids -- sample section from free ebook

Java for Kids -- free 200 page eBook -- by respected Java developer

Going to the moon (Greenfoot game) -- tutorial

Greenfoot Tutorials