For me individually.
Physically: I'm a basically straight female who is very turned on by broad shoulders on men that taper to a narrow waist.
Personalitywise: A man who is a thoroughly mature adult in every way - has excellent communication and conflict resolution skills, isn't manipulative, exploitative, dishonest, self-centered, or un-self-aware, who is compassionate and genuinely motivated to be the best person he can be. A very easygoing approach to life and a deep love of classic rock also don't hurt.
Other: I'm also stupidly turned on by a man who can sing with incredible precision, skill, massive amounts of power, and powerful emotional expression.