OldComputr is giving a free PDF of the book, Commodore VIC 20: A Visual History. 
A book about the computer that made Commodore enter the home market (PDF edition). Many pictures of the VIC 20 revisions and peripherals, plus restored box art images of all the cartridges sold by Commodore for the system.
Another free one (PDF) is on the Commodore Tape Recorders
Commodore Tape Recorders shows all the cassette drives that were used with the Commodore 8-bit line of computers: from the first one in the PET 2001 case to the model 1530 that many of us used to load games on the Commodore 64. The models are presented in the most probable chronological order, with an image of the device and scans of the manual covers. Known variations and technical specifications are shown for each model.