Programming the 6502, 3rd ed., Rodnay Zaks
Programming the 65816, William Labiak
Both for $8+shipping USPS media mail from 97124.
Amazon lists Labiak's book for $300+ from another seller. Go figure.
http://picasaweb.google.com/simplepractices/FSBooks#5325446267684766098
http://picasaweb.google.com/simplepractices/FSBooks#5325446273288278962