Lawrence Krauss makes the case for a flat universe, where the total amount of mass-energy in the universe is and always has been zero.
I've made cuts also in the middle to get it under the 15 minute limit. The video can be seen in its entirety here: http://www.youtube.com/watch?v=7ImvlS8PLIo. Another version, a little shorter, and perhaps also better, can be seen here: http://www.youtube.com/watch?v=rdvWrI_oQjY&feature=related.
