The Beak of the Finch by Jonathan Weiner is also a good one. This book has nothing to do with secularism, though. It is actually about evolution but the implications are obvious. Written for the layperson, it gives great arguments to support the science of natural selection.
I teach English at Valley High School in West Des Moines. I sit on a committee that allocates funding to teachers with innovate ideas that need funding outside of the normal budget. Just yesterday I'm proud to say we allocated funds for
The Beak of the Finch in one of our biology classrooms. Despite all the ridiculous garbage we hear virtually weekly about "warning labels" and "Intelligent Design" theory being forced on school districts, evolution teaching is alive and well. B)
I think the National Center for Science Education's
Evolution vs. Creationism is a very handy and up-to-date book as well. I also love Dawkins's
The Blind Watchmaker.
Rob