http://www.eff.org/awards/coop
The Electronic Frontier Foundation (EFF), the first civil liberties group dedicated to protecting the health and growth of the Internet, is sponsoring cooperative computing awards, with over half a million dollars in prize money, to encourage ordinary Internet users to contribute to solving huge scientific problems. Through the EFF Cooperative Computing Awards, EFF will confer prizes of:
$100,000 to the first individual or group who discovers a prime number with at least 10,000,000 decimal digits
$150,000 to the first individual or group who discovers a prime number with at least 100,000,000 decimal digits
$250,000 to the first individual or group who discovers a prime number with at least 1,000,000,000 decimal digits