gpm:
gpm man page, gpm FAQ, source code file mice.c
XInput:
XInput HOWTO by Owen Taylor
XFree and Wacom:
XF86Config man page
Frederic Lepied's site
Wacom-USB-mini-HOWTO by Arnauld Claden
USB-'Micro-HOWTO' by Semyon Sosin (intuos related)
much, much, e-mails...