When it comes to Jazz, the Penguin Guide can't be beat. It offers the most complete, up-to-date catalog available on the market, covering an exceedingly broad range of jazz artists from around the world. Unlike other discographies, which tend to be American centered, Richard Cook and Brian Morton cover many European, Asian, Latin and African musicians, which will greatly expand your musical range. The guide tends to cover CD's that are in print, so out-of-print CD's and albums are not covered, except in the lengthy biographies the authors have prepared. They also have a very good rating system, which will help you to decide what to pick to add to your collection. I have found these guides to be invaluable aids over the years, keeping my past catalogs, as out-of-print CD's tend to be dropped from the discographies to make room for new releases.