I stumbled upon this site. It has 110 financial calculators for all sorts of stuff.I thought some of them were pretty cool.
http://millionairemommynextdoor.blogspot.com/2007/08/110-personal-finance-calculators-fast.html
http://millionairemommynextdoor.blogspot.com/2007/08/110-personal-finance-calculators-fast.html