A gamma ray burster detected a week ago by the NASA Swift satellite and designated GRB 090423 (CNN article here) marked the discovery of the oldest known object in the Universe -- a supernova of a giant star about 600 million years after the beginning of the Universe itself. This object is about 13 billion light years away (red shift z = 8.2), about a billion or more light years more distant that the most distant quasars (z around 5 or 6). This object is important because it and others like it will provide a way to probe the earliest generations of stars formed in the cosmos.
A more recent bang in the sky was SN 1006 -- a star about 7,000 light years away that went supernova on April 30, 1006 -- 1,003 years ago. For calendar nazis, I understand that today is not the actual anniversary due to the Julian-to-Gregorian conversion. This object was somewhat smaller in scale than the GRB 090423 blast, but still pretty substantial, making it very probably the brightest star (other than the sun) seen by human eyes.
Above, the Chandra image in x-rays of the supernova remnant a thousand years after the blast. The bubble has expanded to a diameter of 20 parsecs -- over 60 light years. Below, a Hubble image of a ribbon of gas and dust from the same nebula.