Mr Calculator Range of calculators including: simple arithmetic, hexadecimal, conventional keypad, mortgage payments, linear measure and more. To be used asis or added to your web site. 
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. 
Calculators.org Free calculation tools helping users to estimate, compute and compare credit cards, financial and retirement savings, the payment amount for auto, home, business and commercial loans, weight loss, body mass index and advanced mathematics. 
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. 
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. 
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 

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. 
Quick Math Automated service for answering common math problems. Provides an array of calculators from algebra, equations, inequalities, calculus, matrices, graphs, to numbers. 
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 
 