everything you would want to do know about barcodes and then some:
http://www.barcodeart.com/links/coderef/barcode_resources.html
http://www.barcodeart.com/front_page.html
http://en.wikipedia.org/wiki/ISBN

become a librarian (and a distance ed comparison)
http://www.becomealibrarian.org/DistanceEdComparison.htm