General (All models)
MCA Enthusiast's Page  THE place to find .ADF files.  Some solutions to common PS/2 problems. Peter Wendt is the Godfather of the MCA Mafia.
The PS/2 Page  Run (loosely put) by Dennis Smith. Great selection of Refdisks and Adapter/Options files.
Linux on a PS/2  By Su Wadlow (owner of >30< 95s. I am awed)
Tavi PS/2 pages by Bob Eager.  Some new MCA utilities (More, more!)
Darren Wright's MCA Linux Discussion (or Obssession)
MADMax  By Tam Thi Pham  Some very interesting complex mods.. 
Computercraft PS/2 Resource Center By Anthony B. Olszewski  
Canada MCA Network Promising start by another Canuck

Specific
P70 The P70 Project by  Jim Shorney  Some kick-butt CPU mods and replacements...
8543 (L40SX) by a Canuck  Alpha base, come in alpha base...
8560 Jason Whorton returns to the fold..
8580 Take a gander and leave comments for Fred Spencer
9556  Web site running on a 9556 by Grzegorz Mazur 
9576 /9577  About time! Dennis Smith. 
9595  chaos barely controlled by Louis Ohland. An ecclectic brew of everything that can go into a model 95 (or 90) including Jolt Cola and coffee. Also commands the MCA Militia.
95 Side Cover Fan by Jim Shorney. Jim has put a little time into a mysterious subject.

Any other Models? The 56/57s, 50s? ... So much to do, so little time. If you have a site on a PS/2 model, tell me!