Math.com A variety of calculators including: basic, scientific, square root, fractions, decimals and more. Also find math resources and tools such as practice tests, games and homework help. 
Calc 3D JavaScript Vector, Matrices and Complex calculators. A program for calculating 3dimensional vectors, matrices, complex numbers and quaternions. Features addition division, subtraction, skalarproduct, unit vector, multiplication, length of a vector 
Specialist Calculators Huge assortment of calculators including those for specific energy, spread rate, viscosity, specific heat capacity, length, area, volume, mass, temperature, angles, cost of living in several different countries and more.http://www.projects.ex.ac.uk/trol/scol  site info 

Coggit Scientific and standard calculators, financial pricing, currency, high school maths, household finances, property, tax and conversion tools. Registered members may save, customize, and operate multiple tool instances on one page. 
Wessa Mathematical statistics and forecasting calculators including an equation plotter, multiple regression modeling, and a variety of descriptive statistics from variability and concentration to percentiles and correlation. 
Basic Mathematics Covers basic mathematic techniques, including graphs, multiplication table, decimals, perimeters, fractions, exponents, geometry and area of shapes, along with a selection of calculators and math resources. 
Quick Math Automated service for answering common math problems. Provides an array of calculators from algebra, equations, inequalities, calculus, matrices, graphs, to numbers. 
Convert It A conversion and calculation center filled with a large variety of measurement and calculator tools, including: currency, finance, date & time, metric to feet, miles to kilometers and more. 
Math Warehouse Interactive math lessons, calculators, charts and games, worksheets, newsletters and discussion forum. 
Mega Converter 2 Discover how many seconds old you are, the difference between a gallon in the USA and a gallon in the UK, how many nanometers in an inch, how many quarts in a chaldron and more. Handy scientific calculator is also available. 
 