If you're not too keen on using the calculator on your PC, you can always try out Google's search based calculator. They've now extended its functionality by rolling out a full on 34 button scientific calculator.
It's everything you need in a calculator, granted most people don't really have the need for a scientific calculator. It's got trigonometric functions, logs, powers, pi, Euler's numbers and factorials.
Google search also works as a graphic calculator, which means most software calculators can pretty much hang up their towels now. [Google via Verge]