People nicely covered it here. A few other additions:

(a) Why is Sex Fun (http://www.amazon.com/Why-Sex-Fun-Evolution-Sexuality/dp/046...): covers the history of human sexuality

(b) The Prophet: http://www.katsandogz.com/gibran.html

(c) Demon Haunted World by Sagan http://www.amazon.com/Demon-Haunted-World-Science-Candle-Dar... is a nice place to explain the method of science

(d) Sleepwalkers (http://www.amazon.com/Sleepwalkers-History-Changing-Universe...) gives you an idea of how we humans,err,sidetrack and ultimately come to explaining the universe

That should be enough for this summer

This seems like a good opportunity to recommend the book "Why is sex fun?" by Jared Diamond.http://www.amazon.com/Why-Sex-Fun-Evolution-Sexuality/dp/046...

(Or apparently "The Third Chimpanzee", some reviewers claim that is a superset of the book).