I bought a mint C64 off of ebay last year, included was it's original Programmer's Reference. It immediately had me missing the afternoons where the limited functionality and simplicity of it all invited you to peek and poke your way around the system trying to coax music and art out of the hardware. Even people who weren't 'savvy' understood this, ex: in the 6th grade our librarian gave us simple programs to type in and encouraged us to change it.