This looks interesting:

In September of 2005, an unprecedented “blog swap” took place between an atheist site and a Christian one. Chad from Eternal Revolution and “I Am” from The Evangelical Atheist agreed to post to each other’s sites in an effort to improve the understanding of each side by the other. The exchange was considered an overwhelming success, and all involved wanted to find a way to keep the dialog open. The GOD or NOT Carnival was born.
…
GOD or NOT is a rotating monthly carnival. Every other Monday, it is hosted by a different blog, alternating between theist and atheist sites. Any theist site is eligible. It need not be Christian. Each carnival has a different theme, featuring posts that deal with a given religious issue. The theme for each carnival is chosen by the previous host with approval of the carnival administrator. The schedule for upcoming editions can be seen below.

I wish I had time to participate.
(Link via Once More Into the Breach)