Since I don't think that I'll ever fix every last vertex, I thought I'd better just get this out there as it is. I've managed to fix six different head models:
PMHH01 - fixed the tongue (it would clip through the cheek when he turned his head)
PMHC04A - fixed the neck where a gap forms when the head turns and reduced the amount of stretching on the back of the hair. Sorry, but I couldn't fix the eyes clipping through eye socket when sleeping.
PFHC01 - fixed the hair beside the ears where a gap forms. Also adjusted the verticies of the ponytail.
PFHC03 - (TSL uses her for NPC) fixed the inside of the mouth so it doesn't clip through the jaw.
N_DaraalaH - (NPC) fixed her left eyelid that stretched when her head turned either way.
N_BrnModulH - (NPC) fixed the back of the head and neck that deforms when the head turns.
I did try to fix some other head models, but wasn't successful.