And one more...
Check out the Web site of Dr. Robert J. Bradbury. He has some very intriguing notions on alien life and how its intelligent manifestations may operate in the galaxy:
http://www.aeiveos.com/~bradbury/CurrentWork.html
And though you probably already know about it, have you seen the December issue of National Geographic Magazine on Other Earths?
http://magma.nationalgeographic.com/ngm/0412/feature4/index.html
