Calculate resister values on a webpage here or here.

 or...

Download the Resistulator 0.1

a Mac OS X Dashboard Widget

About Resistulator

A resistor calculator. It calculates the value of a resistor from the sequence of colored bands painted on the resistor. It also displays the corresponding color sequence when a resistor value is entered. 

Instructions:

To enter a color sequence, click each colored band to cycle through the possible colors. You can look up a color sequence by entering the numeric resistor value from the dropdown menus when the widget is in expanded form. The widget is resized by clicking anywhere on the green background.