Links

Videos

Calculating Annuities  (time: 6:18)
http://www.youtube.com/watch?v=-pdMJdm_JjA

Using a calculator to find a sinking fund - Note: the keys you press will vary depending on the calculator that you are using. (time: 1:58)
http://www.youtube.com/watch?v=u4-_bKgUFnw 

History

This is one of the best all around sites that I have found. It is titled "The MacTutor History of Mathematics Archive."
http://www-history.mcs.st-and.ac.uk/~history/

This is an award-winning site that links to all sorts of mathematics information.
http://archives.math.utk.edu/

Newton:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Newton.html

Leibniz:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Leibniz.html

Reference Topics

There are a multitude of sites to help with retirement planning. Here is a samples:
http://www.troweprice.com/retirement

The annuity formula in the book is actually called an ordinary annuity. This is the situation where the payment is made at the end of each payment period. There is another type of annuity known as an annuity due which deposits the payment at the beginning of the payment period. This site provides a calculator of this type of annuity:
http://www.moneychimp.com/articles/finworks/fmbasinv.htm