Pearson, J. P. (ed.), Digital At Work, Burlington, MA: Digital Press, 1992.
A survey of DEC's accomplishments over a 35-year period.

Bell, C. G., Mudge, J. C., McNamara, J. E., Computer Engineering: A DEC View Of Hardware Systems Design, Bedford, MA: Digital Equipment Corporation, 1978.
A classic engineering reference on DEC hardware design philosophy.

Article on CHM's PDP-1 restoration project.
PDP-1 documentation.
Gordon Bell's documentation.
Spacewar! simulator created by Barry Silverman, Brain Silverman and Vadim Gerasimov.