Very interesting thread and a hard question to answer...

First of all,i believe that for a relationship to work out,you have to like the person both physically and mentally. Yes,I know that ''looks don't matter'',but keep in mind that when you first see someone,looks is all you can perceive. It's just natural,why would you choose someone who is physically not that exciting to you over someone who you do find exciting. Of course,if you don't like the individual as a person,you definitely won't be able to have a happy relationship with them. So,to be truly happy,I believe both parts have to click. There are always exceptions of this,but this is the case in most scenarios.
As far as looks go,I like shorter girls,I don't know why,but I just find them more attractive. Hair and eye color don't matter as long as she they look good on her and fit her. Another very important part is teeth,if she doesn't have good teeth,than it's not gonna work out,but hey,maybe that's just why I'm gonna be a dentist.
As far as personality goes,I'd like to cancel one thing out right away,I do not like it when girls are trying to be the boss in a relationship. It has happened to me before and it's definitely not gonna work out. Friends like that are okay,but in a relationship, nah-ah. Of course,I like girls that are morally and ethically on my level,I don't like it when she's inconsiderate of whatever it is that I care about. Sense of humor plays a huge role,if a girl can't laugh with you,than she probably won't be there for you in whichever other state of mind and feelings you find yourself in. I don't like it when someone is trying to look over my life 24/7,because obsession is not a good trait,lol. My girl should be able to accept whatever it is that I do,and I do a lot of crazy stuff,so if she's worrying too much about it,I don't think it'd be good for neither me nor her to be together. So yeah,just laid back,not afraid to give in the lead,funny and considerate.
There is one more thing I'd like to add to my description,I love girls that are athletic,for instance dancers.
So a girl that I would fall for is like the blonde girl in this song that you see from 2:07 to the end.
http://www.youtube.com/watch?v=cQyGYdRqulQ