Some websites I use to help identify buses:

North American Buses:
http://cptdb.ca/wiki/index.php?title=Main_Page
http://www.etspe.ca/index.html


South American Buses:
http://todoxautobusweb.tripod.com/
http://www.valespbus.com/
http://www.galeon.com/cyberbuses/

Japanese Buses:
http://www5e.biglobe.ne.jp/~iwate/vehicle/extra/primer/