In Game Flavor

(Do not put this in the description-- You may, however, want to use 
it in game as a mannerism)

bass (deep)
bellowing (loud) 
booming (deep and loud)
breathy (with much breath, quiet, husky)
childlike (high-pitched, quiet)
cracking (adolescent/pubescent)
croaking (rough, coarse voice.  Think Yoda)
cultured (having musical tones and clear pronunciation)
deep (low)
drawling (with slurred, drawn-out syllables (typical Southern))
droning (boring, monotone, Think Ben Stein)
dulcet (Sweet to the ear; melodious; harmonious)
falsetto (high-pitched-- typical 'fag-lisp' parody voice)
gravelly (sounding like gravel falling)
grating (harsh, gravelly)
gutteral (very low, almost not human)
harsh (coarse, hard on the ears, grating)
hoarse (grainy, gravelly)
hollow (sounding hollow, almost echoing)
husky (deep, breathy, lusty)
inflectionless (without accent)
lilting (with constantly changing tone)
monotone (with never changing tone)
nasal (twanging out the nose)
ponticello (see cracking)
powerful (clear, loud, carrying)
purring (quiet, smooth, almost like a cat's purr)
quavering (shaking)
rasping (almost a whisper, gravelly, more air than voice)
resonant (carrying, vibrating)
scabrous (harsh, not musical)
shrill (high-pitched, harsh)
sonorous (Loud-sounding; giving a clear or loud sound)
soothing (low, calming, smooth)
spluttering (stumbling over the words, often spitting)
squawking (just like it sounds)
squeaky (just like it sounds)
thin (a voice almost lacking substance)
throaty (coming from the throat)
tremulous (shaking, quavering)
velvety (soft voice with deep tones)
wheezing (with a breathy wheeze)
whining (nasal, high-pitched, annoying)

and, if you're musically inclined, you can use tenor, soprano, 
alto, etc, as well.