Mathematics and calculators

Abacus

Detailed introduction to the Abacus. History, interactive tutorial, etc.

AMSER

Applied math and science education repository. Links to outstanding resources.

Brightstorm: Math

More than 2,000 short-form online video lessons by professional math teachers.

Double Division

Very creative variation on long division that reduces common frustrations.

Euclid

Theoretical and applied mathematics and statistics journals.

Figure This!

Interesting math challenges for middle-school students to try at home.

Free Math Help

Math lessons, math games, and math help message boards.

Illuminations

Math resources for teachers, educators, and administrators.

Math Dictionary for Kids

Very creative and concise guide to hundreds of math concepts.

Math TV

Professional video lessons in mathematics. Covers basic math through calculus.

Mathworld

Authoritative resource for math definitions and explanations of concepts.

That Quiz

Hundreds of free online quizzes to test your math knowledge.

Plus Magazine

Articles on mathematics and its applications to science, art and society.

The Math Forum

Mathematics library and learning center by Drexel University.

Triple A Math

Interactive math lessons on subjects ranging from addition to exponents.

WebMath

Generates easy-to-understand explanations to math problems in real-time.

Bloomberg Calculators

Auto, investment, mortgage, retirement, and loan calculators.

Convert.net Online unit measurement conversion and evaluation of math expressions.
Convert-me Quick and easy online weights and measures conversion.
e-Tutor Graphic Calculator Visually graphs functions of x entered in string format.
Web2.0 Calculator

Trigonometry, matrices, complex numbers, unit conversion and more.

WebMath

Calculates answers and provides easy-to-understand explanations to math problems.

Wolfram Alpha

Computes answers using built-in algorithms and a growing collection of data.

XE Currency Converter

Currency and foreign exchange calculations using live, mid-market rates.