BBC NEWS | Science/Nature | Deep space probe says farewell -- "After more than 30 years in space heading away from Earth, Pioneer 10 has sent its last signal home."
The full article is a great summary -- launched in March 1972, it's official mission ended 25 years later in March 1997, but NASA and JPL have continued to receive signals from it.
For further reading, it looks like the Pioneer mission home page on Nasa.gov would be a good start. (However, at this time their server is not responding.)
Via [Dave]