I often use the calculators at JavaCalc for any financial calculation needs. Things I like about this site:

* It’s free
* I haven’t found any calculation errors with any of the calculators I’ve used
* You don’t transmit any data to the site — the calculators are Java applets that run locally on your machine.

If you look closely, you will find that most major financial sites license the calculators from JavaCalc. Pretty cool, huh?