This week Nathan Seiberg of the Institute for Advanced Studies, Princeton gave the physics colloquium. You have probably heard his name in connection with the Seiberg-Witten theory (which revolutionized areas of both theoretical physics and mathematics), and from Seiberg duality (which gave us a new understanding of strongly coupled field theories).  His talk explained the cosmological and particle physics motivations for supersymmetry, and new ideas about how supersymmetry can be broken if the vacuum of spacetime is unstable.  You can see copies of his slides here.