Roger Hood’s The Death Penalty: a WorldWide Perspective is a great book.  This is true, even if it may be in need of a revised edition, given that this version was published in 2003. 

And, if you sign up for a free trial at Questia.com, you can read his book for free … this is a great thing.  Here’s Amazon.com’s description of Hood’s work:

This is the completely revised and updated third edition of Roger Hood’s classic study on the death penalty. In it he surveys and analyses the status of the death penalty as a punishment worldwide, taking into account the changes that have taken place during the six years since the last edition was published. This new edition is especially valuable at a time when more and more countries are joining the movement to abolish the death penalty worldwide.