Seriously, think about it. Don't just give some generic answer like: Blonde, blue eyes, big titties, w00t!!! She teh roxxor!
Go into personality if you want to. Anything really that does it for you I guess.
For me, I like a smart, petite girl. Hair color doesn't matter to me, as long as it isn't all raggety, or split-ended. I like hair to be
at least shoulder length, anything shorter is unacceptable.

I like being able to put my hands through their hair easily and just look into their eyes.
Eyes are huge for me. If your eyes catch my attention, that is a HUGE plus. Again, color doesn't really matter, because I find beauty in all eye shades. Green eyes are beautiful, blue eyes are captivating, and those big brown eyes just make me melt. As you can see, I don't discriminate.
I used to be a big advocate of taller girls, for I myself am 6'2", but lately, I've been finding a lot more comfort in shorter women, more along the lines of 5' - 5'4". I like being a lot bigger than them, it makes me feel more important, like they really depend on me for protection. That and of course, their bodies fit so much easier in mine when getting our groove on or just snuggling.
I say smarter, because there is nothing worse than talking to girl that is dumber than a fucking door knob. If you have to constantly force conversation, that relationship is going nowhere, and fast...
I also look for girls that aren't always on the move and have to do something. Sometimes, I just wanna relax, watch TV, and sit there, doing nothing but enjoying each other's company.
I won't go into anymore, for I don't want to take all the good qualities away from others, but I'm sure I will add more, and simply agree with others when the time is right.