Generally, non-religious people choose to homeschool because of lack of confidence in the educational system, a child's special needs, or because they want to share the child's life and let her grow in freedom. There are a lot of unschoolers and semi-unschoolers in this group.
Here are a few choice resources to assist those who want to learn in freedom. More to come as they appear!
Downing Family Homeschool Page
The Natural Child Project
National Home Education Network
Butch's Secular Homeschooling Blog
Growing Without Schooling
Boards and Lists
VegSource Secular Homeschool Board
Free-Thinking Home-Educating Families
Rose Rock Global Homeschool Network
Secular homeschool support
Huge list of secular curriculum publishers
Core Knowledge and Homeschool