I wasn't able to find it but a search on google found the following which is very interesting:
American Religious Identification Survey
It contains the following table. It doesn't list who goes to church on a weekly basis, but I think puts to rest the argument that 2/3s of Republicans do and only 1/3 of Democrats:
The Jewish figure is a killer. 56 per cent Democrat?!
What's up with Jehovah's Winesses? Is there something in their faith that discourages voting?