I think there is an element of 'opposites attract' for some people.  I'm one of those Nordic-looking guys, but I find blue-eyed blonds generally the least attractive to me personally.  Obviously good looking ones are good looking, but plain Asian women and slightly above-par African women are more attractive to me.

To some extent this might be explained by a propensity for many higher creatures to be compelled to hybridize.  In times past (e.g., the hunter/gatherer stage where most of our behaviors probably developed), there was a genuine need to seek as much diversity as possible to avoid inbreeding.  I personally feel an above normal interest in procreating when I travel, and it seems to turn my opposite-sex travel partner on as well.  I hypothesis that there is an evolutionary and biological explanation for this along the lines of what I described.