Just got a nice software that might be useful for hobbyists and professionals..
Electronics Assistant is a Windows program that performs electronics-related calculations. It includes a resistor colour code calculator, resistance, capacitance and power calculations and more. Details of calculations can be saved or printed. It provides all the functions found in the calculators section of this site and more in a stand-alone user friendly program..this new version 4.2 includes the following new features: New 555 timer, voltage regulator & RC filter calculators Enhanced series / parallel resistance & capacitance calculator Calculation of preferred capacitor values with a choice of series from E6 to E24 Full compatibility with Windows 7 32-bit & 64-bit Other enhancements & bug fixes Other features include saving or printing of calculation reports, calculation of preferred resistor values, links to open Windows Calculator and up to 3 user-defined programs from the toolbar, hideable theory and formula information panels and full built-in help..
In case you're concerned about downloading an unknown .exe file (you should be!), here is the page describing the Electronics Assistant program. It's safe.