Acererak 20
Asmodeus 24
Demogorgon 24
Graz'zt 14
Iggwilv 14-2=12 Because this is clearly the dumbest name on the list.
Iuz 27
Lord Soth 22
Szass Tam 14
Tharizdun 22
Tiamat 23
Venger 5+1=6 Because the old D&D cartoon was lame-tastic.
Vlaakith 12
Zargon 17