Two common calculators for electronics/electrical use:

Ohm's law calculator/Watt's Law calculator: figures any 2 unknown values given 2 known values

Resistor calculators: figures bands given value or value given bands. For 3, 4, & 5 band resistors

* Preferences/lock functions allow values to either autorange to appropriate SI units or remain fixed

* Resistor calculator automatically determines 3, 4, or 5 band

* Clean, intuitive interface

*** To the few who have commented that it's "stupid" to have the "Rate" button where it is, please stop && think. You don't HAVE to rate it before using it, nor are you even being asked to. You will notice that there are 2 buttons. This is the "About" dialog that is shown the first time you run any new version or tap the "About" menu item. Please think before you speak. Thank you. ***

Paid app "Electrist" identifies EIA standard values, as well as adds many more calculations. See for yourself:
https://market.android.com/details?id=com.redbinary.electrist

Recent changes:
1.71 [Mar 3, 2012]
+ added some exception handling and better handling of parsing numbers from input strings