There are several theories to explain the differences men and women have in selecting a mate.
Epstein and Guttman (1984) reviewed 3 types of these: sociobiological, sociological, and psychological. None of these theories provide a complete model, unfortunately, and Epstein and Guttman recommend a multivariate approach.
Geary et al (2004) focus specifically on evolutionary theories in their review.
Experimental data show that there do tend to be differences in the criteria men and women use.
Feingold (1992) finds that women are more likely to focus on non-physical characteristics such as socioeconomic status and ambition.
Kamenica and Simonson (2006) [edit: aka
Fisman et al, 2006] found that women's (but not men's) selectivity varies depending on group size; that is, women become pickier the more options they are presented with. Kamenica and Simonson also found that women placed more emphasis on race than men did, however this may have been confounded with perceived socioeconomic status.
For much of my adult life, I've been so concerned with making an equal contribution to my relationships that I've probably overshot. I'd have a much easier time living with being a sugar daddy than a kept man, or at least I like to tell myself so. However, there was one autumn when I threw pride to the wind and took advantage of mate-selection differences, and I'm not particularly proud of it. In the fall of 1996, I ended up flat broke, due to an uninsured car accident. Personal ads for women are generally free, so I placed an ad and went on 2-3 dates per week, letting men pick up the tab for most of my eating. I had no intention of seeing these guys again, and I didn't really represent my personality in the ads, because I wanted the type of man who would pick up the check, not the type I'd actually date. After a month or two I got really disgusted with myself and stopped, but I don't think I've ever really forgiven myself for it.