Quite simply the best version of Gregorio Allegri's Miserere mei, Deus.
This is with out a doubt the most beautiful and haunting piece of choral music there is.
February 2010 Update.
As my few lines have been of help I decided to expand a little on my thoughts above.
What makes this recording stand out above the rest?
Well the Kings College version of 1963 although excellent does I feel show its age in terms of recording quality and also that it is sung in English not Latin. This 1983 recording has that same warm mellow sound of the 1963 one, but is sung in Latin. This coupled with perfect recording and mixing just give it the edge I feel over all the other recordings that I have.
If like me you just love listening to this piece of music then I highly recommend the following recordings of Miserere mei, Deus by The Choir of St John's College on their album Meditation, St. Paul's Cathedral Choir on their album The Music of St. Paul's Cathedral and The Choir of New College Oxford on their album Agnus Dei.