An Introduction to the Inquisition
Good place to start

The Inquisition
From the Catholic Encyclopedia, an examination in great detail, including a focus on Spain

The Malleus Maleficarum
The Witch's Hammer, one of the fiercest and most widespread tools for convicting "witches"

Inquisitor's Manual
Not exactly light reading but illustrative

The Inquisition
Good summary from The Galileo Project

The Spanish Inquisiton
Darker, more powerful of the religious movement

The Spanish Inquistion: Fact vs. Fiction
Examination of both sides of the issue

The Real Inquisition
Examines the possibility of myth and politics in the retelling of medieval torture

Torquemada
The Grand Inquisitor of Spain