Cosmic Company: The search for life in the universe by Seth Shostak and Alexandra Barnett (Cambridge University Press, 2003))
The authors ponder the possibility of alien life and the consequences of receiving a signal from the cosmos. They explain why scientists think sentient life might exist on other worlds, how we could discover it, and what it might be like. Entertaining, informative and lavishly illustrated.
Get this book
 

The Phoenix Lights: A sceptic's discovery that we are not alone by Lynne Kitei (Hampton Roads Publishing, 2004)
One evening in 1997 thousands of Arizona residents witnessed a mile-long, V-shaped formation of lights flying in the skies overhead. Dr Lynne Kitei had been witnessing and documenting this phenomenon for months and this book is an exhaustively researched look at the wider implications of this remarkable event, with dozens of astonishing photographs.
Get this book
 

Wonderful Life: Burgess Shale and the nature of history by Stephen J Gould (Vintage, 2000)
An account of a revolution in our understanding of life's history, Gould tells how three obscure British scientists completely changed our view of evolution by discovering a unique group of 530 million-year-old creatures in the Burgess Shale fossil deposit in the Rockies.
Get this book
 

Life's Solution: Inevitable humans in a lonely universe by Simon Conway Morris (Cambridge University Press, 2004)
Morris explores the evidence demonstrating life's almost eerie ability to navigate to a single solution, repeatedly. If these are all evolutionary inevitabilities, then where are our counterparts across the galaxy? The tape of life can only run on a suitable planet, and it seems that such Earth-like planets may be much rarer than hoped.
Get this book