GURPS provides only 6 different stages of looks. Using the same rules found in the Reputation section, characters can easily draft up their own particular look, if they want something more flavorful than ``Attractive.'' Under no circumstances should someone get more than +6 for Looks, and mixing Looks advantages is certainly allowed.
Here are some examples: (same sex/opposite sex)
Pretty (10) = +1/+3
Bosomy (5) = -1/+3
Ruggedly Handsome (15) = +4/+2
Cute (10) = +2/+2 (applicable only for children and senior-citizens)
Nice Elbows (or other feature) (5) = +2/+2, but only noticed ? the time.
Sexy (5) = 0/+2
Plain (5) = +2/0 (other girls feel sorry for you)
Vain (-10, actually an Odious Personal Habit, but it fits here) -3/-1 (``She tries to hard'')
Plastic Surgery/TL (5) +1/+3, only works ? the time. Otherwise people notice it and are unimpressed.
Perfect Scalp (5) = +2/+1 (men only and you must be bald) Captain Picard, Michael Jordan.