Equations

Searchable directory, arranged by field, of equations, constants, symbols and SI units. Also features LaTEX utilities, software links.

http://www.equationsheet.com/

Geometry Formulas and Facts

An excerpt from the 30th Edition of the CRC Standard Mathematical Tables and Formulas, covering the area of Geometry (minus differential geometry), by Silvio Levy.

http://geom.math.uiuc.edu/docs/reference/CRC-formulas/

Math Open Reference

An online interactive Math textbook.

http://mathopenref.com/

Math Tube

Mathematics lecture videos and talks taken from The Pacific Institute for the Mathematical Sciences (PIMS) member universities and around the world.

http://www.mathtube.org/

Math formulas

A large , free online lists of mathematics formulas. Collection of all basic and advanced formulas related to mathematics.

http://www.sciencehq.com/math-formulas/

Mathematics Notes

Exposition of the basic concepts and theory of various subjects including matrix theory, calculus, modern abstract algebra, linear algebra, plane analytic geometry and solid analytic geometry.

http://solitaryroad.com/math.html

NIST Digital Library of Mathematical Functions

Result of a project to provide a modern revision of Abramowitz and Stegun’s "Handbook of Mathematical Functions". The site includes definitions, properties, and graphs of many special functions.

http://dlmf.nist.gov/

Numerical Prefixes

Tables for Greek and Latin number values alone and as a part of other words.

http://phrontistery.info/numbers.html

Platonic Realms

Online resource for the mathematics community: links library, bookstore, quotes, and online articles.

http://www.mathacademy.com/pr/index.asp

Summation Formulae

For polynomials of degrees up to 50, generated using the Euler-Maclaurin method.

http://polysum.tripod.com/

The Math Reference Project

An electronic archive of articles by Karl Dahlke on topics ranging from high school geometry up to graduate level topology.

http://www.mathreference.com/

Tricki

A large collection of useful mathematical problem-solving techniques.

http://www.tricki.org/

Web Formulas

Web Formulas provides collections of formulas used in math, physics and chemistry.

http://www.web-formulas.com/