Links

Videos:

Adding Integers (time: 1:51)
http://www.youtube.com/watch?v=G_c5J8xHPYo

Subtracting Integers (time: 2:08)
http://www.youtube.com/watch?v=rfUIDjLV9Vw

Multiplying Integers (time: 1:15)
http://www.youtube.com/watch?v=_QpVerf19DY

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/

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

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

Reference Topics

Math League's integer site:
http://www.mathleague.com/help/integers/integers.htm#multiplyingintegers

Mrs. Glosser's Math Goodies,TM
This site gives worksheets, exposition, and other practice, but would like to sell you a CD.
http://www.mathgoodies.com/lessons/toc_vol5.html

Fibonacci numbers to represent integers
An interesting enrichment site which used Fibonacci numbers as a base to a numeration system representing integers.
http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonac