Who gives more to charity?

A friend of mine recently stated that Republicans give more to charity than Democrats. Can anyone help me get to the bottom of this issue? I have a feeling that Republican givers include those who tithe their $$ to a megachurch, only to see it used to build a bigger one. That, to me, doesn’t count. I’d love some real data from an independent source, even if I’m ultimately shown that Republicans are better people than me, a frustrated liberal. :-) Help?