i really got a lot out of
"What Every Woman Should Know About Men"
by Dr. Joyce Brothers.
it was written for women obviously,
but if you want insight into the cultural divide between men and women... this will help.
it helped me understand me,
it helped me understand my wife,
and it really had a positive influence on my marriage (23rd anniversary this year).
it is not specifically about sex, but let's face it...
when the relationship is good, the sex is great!
the book is dated 1981 and may not be modern enough for you,
but i still recommend it and i still read it.
i leave you with this quote from the intro to the book...
"As far as male and female are concerned, difference is a biological fact, whereas equality is a political, ethical and social concept. No rule of nature or of social organization says that the sexes have to be the same or do the same thing in order to be social, political and economic equals."