You'll need these two books...
Commodore 64 Programmer's Reference Guide
Commodore 64 User's Guide
and maybe a thrid...
Commodore 1541 Disk Drive User's Guide
Those will have all you need to keep you busy and happy for a long while. You may get the 64 user's guide with your C64, the other two can be found used at ebay, maybe lemon64.com or perhaps Redrumloa has some spares lying around.
Here's an online scan of the Programmer's Guide, but I don't know how complete it is. Lots of good info non the less.
Commodore 64 Programmers Reference GuideYou should be able to do searches and find tons of example code programs and articles on the net to help too..
Plaz