Processors (CPUs, Processor Adapters, CPU Upgrade Modules...)
Memory (error handling, presence detect)
Storage (Floppy, Hard Drive, CD-ROM, Tape...)
   SCSI (adapters, RAID)
Video
Sound
Model "M" Keyboard

Ports and Peripherals
   Keyboard Port
   Mouse Port (YMMV)
      Optical Wireless Mouse
   Parallel Port (Modes, ExpressPrint)
   Serial Port
   Wrap plugs (For diagnostics)
   PC-2-PC Cables (Serial and parallel LapLink cables)
   Joystick Metrics

RTC - Real Time Clock
   PS/2 CMOS Batteries (by Bob Eager and Peter Wendt)
   Reworking the Dallas RTC (thanks to Peter Wendt)
   MC146818 (Clearing the RTC, HW vs SW clock)

Flash ROM memory (late PS/2s only)
IBM PS/2 ASICs List of IBM VLSI Application-Specific ICs