Sites

The Planetary Society (Popularity: )
http://www.planetary.org/
A nonprofit organization devoted to the exploration of the solar system and the search for extraterrestrial life.

The Rise and Fall of Star Faring Civilizations in Our Own Galaxy (Popularity: )
http://www.jrmooneyham.com/ctcta.html
Speculation, based on the Drake Equation, regarding the existence and composition of alien civilizations.

Search for ET! (Popularity: )
http://jvsc.jst.go.jp/universe/et_e/index_e.htm
Interactive Flash tutorial exploring the possibility of and search for life on other worlds.