The PDP-11 Unix Preservation Society - Devoted to the preservation of all information related to the versions of Unix that ran on Digital PDPs. - http://minnie.tuhs.org/PUPS/index.html
Pdp11.org - Dedicated to preserving the history and legacy of the PDP-11 series of 16-bit minicomputers. - http://www.pdp11.org/
The PDP-11 FAQ - Information for those who are enthusiasts, curious, or downright confused as to what the -11 was and is, and how it related and still relates to its world. - http://www.village.org/pdp-11/faq.html
Mentec - PDP-11 operating systems plus layered products and services. - http://www.mentec.com/