The New York Times has a fascinating tool online which allows us political junkies to explore the presidential vote breakdown in counties defined by the characteristics of their population. The “Electoral Explorer” shows the vote in counties with a specified percentage of the population that's black, white, Hispanic, Catholic, Southern Baptist, high school or college graduates, unemployed, over 65, employed in manufacturing jobs, in poverty, as well as median income and population density.
Keep in mind that you’re looking at the vote only in counties that fit the characteristics which you specify. So, just because Sen. Obama won 75% of the vote in Dimmit County, Texas which is 95% Catholic, the national Catholic vote didn’t mirror that trend. However, you can glean a lot of interesting information playing around with this. Have fun!