Update: Videos (68.6KB, 108KB, Courtesy: NASA-DeepImpact)
Deep Impact is a NASA space probe designed to study the composition of the interior of the nucleus of the comet named Tempel-1. Tempel-1 is a periodic comet discovered in 1867 by Ernst Wilhelm Leberecht Tempel, an astronomer working in Marseille, France. The probe was launched on January 12, 2005. After its initial analyses of the comet, the probe separated into two parts (Impactor and Flyby).

Bada Boom! (Courtesy: NASA)Now scientists have successfully crashed the Impactor into the comet:). The goal is to expose the interior of the comet, and thus gather data (using the Flyby) that should tell us a lot about the inner workings of the comet, and also shed light on the formation of our Solar System.
The Impactor is the size of a washing machine, whereas the comet is of the size of Manhattan (14 km long). The collision happened some 83 million miles from Earth:):).
The show is observed by all the major telescopes! It's not just Deep Impact that observed the mission. Every space and ground-based telescope large enough to do the job were watching: Hubble, Chandra, Spitzer, Galex and SWAS space telescopes were all recording the event:). The Rosetta spacecraft, a European probe on its way to another comet (67P/Churyumov-Gerasimenko), also observed and recorded the show:)).
Scientists expect a wealth of data from all these observations. Not only will this help us in our understanding of comets, but it should also tell us more about the origins of our Sun, planets, and ultimately, us:).