This is a great introduction to Julian Simon, one of the greatest economists of the 20th century (and certainly the most under-appreciated).
Simon used hard facts and sound logic to debunk the claims of radical environmentalists who predicted disaster. He showed that overpopulation is a myth, endangered species aren't really endangered, and that freedom and liberty are the keys to human prosperity.
He's pretty cool, and he died way too young. He was a hardcore libertarian too.