Gallup has asked, "If your party nominated a generally well-qualified person for president who happened to be X, would you vote for that person?" for X = {Catholic, black, Jewish, female, hispanic, Mormon, homosexual, atheist}. Below I have plotted their results over time.

Update August 6, 2010: The link to the raw data above no longer has it. But you may be able to get it through some combination of here and here (on the latter link, click through to the second page).