Carl Zimmer has a fascinating entry on skewed sex ratios and the conditions that generate them. As Carl notes there is plenty of data on this, to me the most interesting research that I recall was the predominance of young boys in the graveyards of medieval European peasants, while the reverse is was noted among the nobility (read Carl's entry to see how this fits some of the animal data). On a related note I recently heard through the grapevine that an animal breeding grad student at Washington State University has figured out how to get ungulates to skew ratio toward females by injecting a sugar solution into their "special parts."

Related: Old entry titled "Sex Ratio Fallacies" by David B.

Addendum: My maternal grandmother: six sons, one daughter. My mother: four sons and one daughter. My mother's maternal female cousins? Total of four sons and two daughters.