Consider consulting the Unitarian Universalist Association's "Find a Congregation" web site to locate an agnostic church. The UUA accepts people of all religions and faiths, including Agnosticism.
Agnosticism is separated into two sects: hard agnosticism and soft. Each sect revolves around the idea that nothing pertaining to the soul, the afterlife or the creator is known for sure. The Unitarian Universalist Association embraces Agnostic ideas for those that believe them.
For an non-traditional Agnostic church, consider joining The Church of the Apathetic Agnostic. This church exists entirely online in a forum. While a bit tongue-in-cheek, it provides a welcome space for Agnostics who have not found a brick-and-mortar church.