There is a number of calculators out there, and you can find one for practically any purpose you may have. Your choice should depend on what you are using a calculator for, and what kind of calculations you plan on doing.
Gold Calculator Software Products
MicroTask Computer Services
Apollo Fire Detectors Ltd
Ken Wilcox Associates, Inc.
GPS Utility Ltd.
Myostat Motion Control Inc.
Fluke Electronics Corporation
Quality Assurance Software Sys.