I don't think there is any one answer to this question since different types of men look for different qualities in a woman so the best I can do is speak from my own feelings and desires and tell you what I, personally look for in a woman.
The first thing is the initial attraction and this is not strictly a question of good looks. It's kind of hard to explain attraction for me. Of course a woman with striking beauty can turn my head, but I am not always romantically attracted to her other than she is pleasant to look at. If the personality I like is not there, the attraction dies immediately. As an example of what I am talking about, Paris Hilton has striking beauty, but I wouldn't be attracted to her as our personalities wouldn't jive.
That said, I want to say that it's not necessarily great looks that stirs attraction in me but I want a woman that is good looking and pleasing to MY eye. For me, a lot of times, it's a "look" that she has that I cannot always explain. I am a simple, average type of guy so I guess I might call it the "girl next door" type. A lot of it has to do with how much a girl's sincerity and inner light shows through. It can be a look in her eyes or how she smiles. How a girl smiles can be a window to her soul and if it's right, an extreme attraction. Some girls smile with their mouth and some smile with their whole face, if you know what I mean. When a girl smiles that special smile that lets her inner self show through and I can see the sincerity in her eyes, it can melt my heart.
After the initial attraction, I want to explore more about her personality and her likes and dislikes. I look for a "nice" girl and by that I mean someone that is polite, pleasant, good hearted, etc. I want someone that has a lot in common with me as far as hopes and dreams and what they want out of life and how they want to live life. The more interests in common, the better the relationship will be because I want a partner. I want a companion that I can do everything with and totally enjoy being with her in every endeavor. Having someone that enjoys the same activities for fun and pleasure as well as working toward common goals is the ultimate. I want a mate that is also my best friend.
It also helps to have someone that is on the same intellectual level also. This doesn't mean that I look for someone that has a college degree or some level of formal education, but I want someone that is on a similar level of mind so we can enjoy each other conversationally and are of like mind in matters such as social and political issues, religion, literature, etc.
I also look for a girl that doesn't have extravagant tastes. I want someone that knows how to be fiscally responsible and doesn't blow money needlessly. I don't look for someone that's rich or makes a certain amount of money either. It's not about that. It's more about wanting to be with someone that wants to work together to achieve the same goals when it comes to the question of how to spend money and how to live. I guess I would say I look for someone that isn't into how much money I make, but more on enjoying the simple things in life first. If you have that first, then you can better work together to achieve a higher income level if that is jointly desired.
I have talked about what attracts me to a woman but it's also very important that it be mutual. I want her to feel the same attraction and desire toward me as I do toward her. One sided attraction will not lead to a lasting relationship but if I feel a woman is attracted to me naturally for who I am and genuinely desires to be with me, it makes her all the more attractive to me.
Having a great level of attraction and desire on a platonic level will lead naturally to the next level so I guess I should talk a little about sex. Without going into graphic detail, I want a girl that has the same desires and needs and is uninhibited when it comes to sex. Not only in the types of sexual activities, but also frequency. In my case, after spending too many years with the wrong woman, the fact that miss-matched sex drives can ruin a relationship became painfully apparent (and extremely frustrating, I might add) so this is very important I think. Having a sex life that is enjoyable and totally satisfying to both can be a deeply bonding experience for two people.
So that's my perfect woman I guess. I could go into more detail and delve a little deeper but I guess I should keep it under "book" length.
I think if two people can meet and be mutually attracted to each other and then have the level of compatibility and things in common that I have described, it would be the type of true, undying love that lasts a lifetime. So far she's just a dream. I haven't found her yet. Maybe someday...