Physically? Two things.
First, health and athleticism. Which is unfortunate given that I'm a couch potato.
-Calves are my thing, for reasons I've never understood. I like to see hard, diamond-shaped runner's calves that create shadows when flexed. Drives me mad!
-Tight waist
-Thighs that show distinct musculature when running
-Developed shoulders and triceps
-A figure that is firm and strong throughout
-Impressive stature. Should be 5'8 or taller -- I'd love a woman who could look me level in the eye, not easy as I'm 6'2"
Second, a clean, natural, unadulterated look.
-Clear skin is a must. Freckles and moles are a turn-off.
-Hair can be short, even crew cut is fine, but should not be longer than the shoulder blades. Natural color is preferable. Dyed hair is acceptable as long as it's a color humans actually have.
-Tattoos are gross, with tats of whole sentences or song lyrics particularly repellent.
-And can facial piercings please just DIE already?
-Clothes should be practical, I actually prefer flats over high heels and find sweatpants and t-shirt at least as sexy as strappy lingerie.
-She can be any heritage or color but it's better if she's not pretending to be a different one (white girl with dreadlocks, for example -- eek!).
Mentally/Socially? As Henry Rollins says, 'I want a woman who can sit me down, shut me up, and tell me ten things I don't already know.'
-She reads, probably more than I do.
-Smart, 90th percentile at least.
-Honest to a fault, which I don't consider a fault at all.
-Able to resolve disagreements like an adult, without screaming or diverting into something I did wrong six months ago.
-Can't be a chatterbox. Real conversation is great but nattering drives me up the wall. Can't interrupt constantly.
-Low maintenance. If I have to text her twenty times a day, or regularly drive to her house at 3am because she's having another nervous breakdown, it ain't gonna work.
-Gets at least 1/4 of my movie/show references. Bonus points if she can deliver the next line.
-Makes me laugh at least once every time I see her.
-Never agrees just to pacify me.
-Never disagrees just to wind me up.
-Doesn't give half a shit for trends.
-Isn't extremely political. Or at least doesn't try to involve me in it.
-Not religious. I feel like eventually this would become a problem. I probably know people who are religious and don't say anything about it, but the talkers kind of make up for that. Can't have a conversation with my uncle -- an intelligent, well-read man -- on the subject of evolution. Just can't do it. My mother lost her best friend because everything this friend said, did, or thought had to be about god, all day, every day.
-Understands that I'm a depressed introvert with a bit of a temper. She has to be okay with the fact that I don't always want company, she can't always help, there isn't always a good reason, and it's not her fault.