Pale Blue Dot: A Vision of the Human Future in Space, by Carl Sagan
Life as We Do Not Know It: The NASA Search for (and Synthesis of) Alien Life, by Peter Ward
Darwin's Universe: Evolution from A to Z, by Richard Milner (I'm really just browsing it at this point.)
LoneStarMa recommended Endymion Spring, which just came in, so I'll take a look at that too, plus a friend of mine just lent me The Man Who Mistook His Wife for a Hat: And Other Clinical Tales, by Oliver Sachs. I am particularly interested in the first essay, which deals with prosopagnosia, a condition in which there is an impaired ability to recognize faces.