Fermi Paradox/Drake Equation: Drake's equation attempts to estimate the number N of currently extant civilizations in our galaxy that would be able to contact each other.
Fermi's Paradox: Summary and a few probability calculations.
Fermi's Paradox: Lecture notes from a college cosmology course.
I.T. seeks E.T.: Discusses the Allen Telescope Array (ATA) scheduled to be completed by 2005 and the search for extraterrestial life as it related to Fermi's Paradox and the Drake Equation.
The Drake Equation: Describes the famous formula for estimating the number and character of alien civilizations within the galaxy. Includes an online form that calculates your numbers.