I generally prefer to use online tools. This way they're available no matter where I go (Google for email and files is good this way also).
For resistors, the only site I tend to use is this one:http://www.daycounter.com/Calculators/Standard-Resistor-Value-Calculator.phtml
The only disadvantage to online tools, is if they are down or disappear.
What I like about the above is that you can choose your tolerance and plug in your exact number of ohms. Then it will select the standard value for you and show you how much error there is in the selection. For example if I wanted 930 ohms, the site tells me:
The closest 10% resistor for 930 ohms is 1K ohms.
The error is 7.5 %.
If I determine that this is not good enough, I can try a 5% resistor:
The closest 5% resistor for 930 ohms is 910 ohms.
The error is 2.2 %.
This very helpful if you are designing circuits.