A variety of proofs of the Pythagorean theorem are found at this site. There are also some interesting remarks concerning this theorem:

http://www.cut-the-knot.org/pythagoras/index.shtml

For those of you who think that irrational numbers can be written in some (yet unknown) decimal form, you might want to check out this totally useless web page:

http://antwrp.gsfc.nasa.gov/htmltest/rjn_dig.html

The irrational number is the subject of the following site:

“Pi through the ages,” is an interesting history of the number.

http://www.math.com/tables/constants/pi.htm