Check out this interactive map from The Chronicle of Philanthropy. What intrigues me at first blush is that the darker areas (greater percentage of giving) seems to overlap areas of the United States where you will find more strongly held religious beliefs within the general population.
Does that mean that religious people are more generous? Probably too little data to draw a conclusion, but worth exploration.
Below is a link to a Pew Research web page that shows the United States and location of various stages of religious belief, as compiled from a religious landscape survey (click on image to go to website). There does seem to be strong overlap.