I just finised the The Evil 100 by Martin Gilman Wilcott/Stephen J. Spignesi
The editors of this book have put together a list of 100 undoubtedly evil people (mostly men, but including poisoner Catherine de Medici and real-life vampiress Elizabeth Bathory as well as one or two other women)distilled down to 2-3-page summaries covering their lives, their actions, and usually a little bit about their motivations, though frequently these are facile one-sentence comments such as "infidels cannot be allowed to live." Though body count and continuing influence are important factors, the editors also use a somewhat nebulous "glee factor" and the depravity of a subject's action when determining rank.
pretty chilling book