I'm going to repeat and expound upon what was already said in case there are other aspiring 6502 (6510) machine language programmers out there. These are the books that were already mentioned:
Machine Language for the Commodore 64 and other Commodore computers by James Butterfield Published by Brady Communications
Machine Language for Beginners by Richard Mansfield Published by Compute! Publications
I would also recommend:
Mapping the Commodore 64 by Sheldon Leemon Published by Compute! Publications
Unfortunately they are out of print but are available (used) through Amazon et al and copies were available at last year's World of Commodore. What some subscribers of this list might not know is that these books and quite a few others are available electronically through Project 64 (see <http://project64.c64.org/> for their website.) To save you hunting around, you can find all the books listed above at this URL:
http://project64.c64.org/misc/index.html
A good place to find help if you're learning ML is the Secret Society of Commodore Coders message board. You can find it here:
http://jledger.proboards19.com/index.cgi?board=ssocc
Hope that helps.
-- Golan Klinger <gklinger@xxxxxxxxx> Dark is the suede that mows like a harvest.