Collect a vintage library or want to learn to program? Check these out. These aren't ALL 128 books, but I listed them all here anyway. Some of them are pretty common, but still useful. Others are harder to find and pretty well sought after. I've grouped some of them together for my convenience and hopefully yours:
"Commodore 64 Programmer's Reference Guide"
"JiffyDOS User's Manual"
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362318057
"Commodore 64 Programmer's Reference Guide"
"Commodore 64 User's Guide"
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362319557
"GEOS 128 User's Manual"
"GEOS 128 User's Manual Addendum"
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362320023
"Compute's 128 Programmer's Guide"
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362320988
"Compute's Machine Language Routines for the Commodore 64"
"Machine Language for Beginners" by Richard Mansfield
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362321736
"The Machine Language Book of the Commodore 64" by Lothar Englisch
"The Second Book of Machine Language" by Richard Mansfield
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362322684
"Your Commodore 64" by John Heilborn
"Commodore 128 System Guide"
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362325588
"Advanced Commodore 128 Graphics and Sound Programming" by Stan Krute
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362323855
"Commodore 64 Graphics and Sound Programming" by Stan Krute
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362324250
"Commodore 128 Programmer's Reference Guide"
"Commodore 128 System Guide"
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362326112
"Commodore 64 Computing" by Ian Sinclair
"The Elementary Commodore 64" by William B. Sanders
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362323112
"Commodore 64 Favorite Programs Explained" by Donald C. Kreutner
"35 Amazing Games for Your Commodore 64" by John Mihalik
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120362323503