What is this? This is the sort of list some edgy Christian would put together. I partly take that back; this list is very Atlas Forum
In the modern era you could say Jonas Salk for his medical contributions and or Gloria Steinem for her views on feminism and early advocacy of a lot of current mainstream issues. James Randi was the most effective of the 'skeptics.'
I agree with the inclusion of Carl Sagan.
If your list is primarily Brits making a quick buck fifteen years ago to argue on Christian college campuses that's quite sheltered.