I downloaded the free Microsoft CalcPlus which does standard, scientific and conversions including currencies. If you run windows that is surely even faster and always available to you. Mine is on my quick launch bar.
I have the Google side bar on mine. Since I have a wide screen my browser is full size and I still have room for the side bar. It has the weather, clock, performance meter, calculator, news, maps, and photo slide show.
Kinda cool...