A Companion to Digital Humanities is now freely available in digital form.
This important 2004 book was edited by Susan Schreibman, Ray Siemens, and John Unsworth. It includes chapters by such notable experts as Howard Besser, Greg Crane, Susan Hockey, Willard McCarty, Allen H. Renear, Abby Smith, C. M. Sperberg-McQueen, John Unsworth, and Perry Willett (to name just a few).