The ones I use regularly are:
fillet zero (defun c:fz () (command "fillet" "radius" 0 "fillet") )
Purge all with no dialogue box (defun c:pu () (textscr) (command "purge" "all" "*" "no" ) )
Audit and autofix no dialogue (defun c:au () (command "audit" "y") )
Line convert to pline and join (defun c:pj () (command "pedit" pause "j" pause) )
Attribute set, paper space and zoom to fill screen (defun c:pz () (setvar "tilemode" 0) (command "pspace") (command "zoom" "e") (command "zoom" ".95x") (command "layer" "s" "0" "") (command "mirrtext" "0") (command "psltscale" "0") (command "regenauto" "on") )
I like the two you posted very much and will be stealing them :).
One other thing, a good way to expand on available keyboard shorcuts is to use one letter twice. Rather than make the circle command CI and having to go across the keyboard to envoke it, I chose to use CC instead as it is much quicker, same thing with the mirror command (MM).
Mostly for me it helps when you need to look at two drawing side by side, otherwise a half an inch doesn't really make that much of a difference.