In 1994, two Swiss astronomers, Michel Mayor and Didier Queloz, announced the discovery of a planet having about half the mass of Jupiter in orbit around the star 51 PEG. This was the first extra-solar planet discovered around a sun-like star.
Exoplanets: The Hunt Continues!
A press release from European Southern Observatory (April 4, 2001) about the discovery of 11 more exosolar planets.
exoplanets.org
A site maintained by Marcy, Butler, et al
Astronomy Picture of the Day, December 1, 1995
Astronomy Picture of the Day, June 14, 2002
UC Berkeley Press Release on 55 CNC
A laboratory exercise on 51 PEG
Searching for Extra-Solar Planets
Yahoo Search on "extrasolar planets"
The Astrobiology Web: Extrasolar Planets
Exoplanet Mass Ratio Calculator