The Last Days on Earth is a 20/20 science special which aired on ABC in August 2006 and has been aired on The History Channel.
The show counts down the seven most likely ways in which the world could end, including gamma ray bursts, machine rule, asteroids, super volcanoes, nuclear war, pandemic flu, and climate change. It includes input from a number of scientists including Michio Kaku, Neil deGrasse Tyson, Stephen Hawking and Kevin Warwick. In 2007 it received an Emmy nomination for its graphic and artistic design.

These are organized from least likely to most likely:
Number seven was actually two alternate views of what could happen to a star and how it could destroy life on earth.
Death of a Star: Gamma-Ray Burst
Death of a Star: Black Hole
Intelligent Machines
Supervolcano
Asteroid
Nuclear War
Plague
Climate Change (Global Warming)