Calculator Central
http://www.calculator.com/
More tools than you'll ever need. This is the kitchen sink.

Cost of Living Calculator
http://www.homefair.com/homefair/cmr/salcalc.html
Compare cost of living in two different US cities.

Currency Converter
http://www.x-rates.com/calculator.html
Converts to and from foreign currencies.

Distance Calculator
http://www.indo.com/distance/
How far is it from x to y? Don't know why this one comes from Indonesia, but it works!

Financial Calculators
http://www.mortgageloan.com/calculator/
Calculators for loans, investments, debt, taxes and retirement.

Inflation Calculator
http://data.bls.gov/cgi-bin/cpicalc.pl
Tool from the Bureau of Labor Statistics allows you to adjust for inflation.

Loan Payment Calculator
http://info.aavirtualoffice.com/Calculator/
Estimate monthly payments.

Online Conversion
http://www.onlineconversion.com/
Distance, temperature, speed, volume: convert them to your unit of measurement.

Percent Change Calculator
http://www.newsengin.com/
An essential tool for putting change in context.

Percentage Calculator
http://www.math.com/everyone/calculators/calc_source/percent.htm
What percent is x of y? This tool makes it simple.

Statistics Tests
http://statpages.org/
Helps you select and perform the right test for the right information.

Tax Calculator
http://www.heritage.org/research/features/taxcalculator/
Conservative think tank calculator simulates results of the Bush tax plan.

Temperature Converter
http://www.futuresource.com/weather/cfcalc.asp
Simple to use: plug in either Celsius or Fahrenheit and hit the calculate button.

Time Converter
http://www.timeconverter.com/cgi-bin/tzc.tzc
What time is it there? Plug in time zones or major cities and find out.

Body Mass Calculator
http://www.kcnet.com/~marc/bmi.html
Just in case anyone really wants to know....