Forensic Discovery by Dan Farmer and Wietse Venema
Just a quick FYI for those unaware, this has been released and I picked it up recently -- like today! :D. Given who the authors are it looks interesting and I have high expectations. Additionally, this isn't just about theory but also hands-on labs for those learning. It is heavily oriented towards the *nix environment, with a lot of the hands-on samples from Linux.
For those unaware Dan Farmer and Wietse Venema are probably most well-known for the creation of SATAN (which has been used as a basis for SAINT, SARA and other vulnerability scanners)and The Coroner's Toolkit.
Dan Farmer's Website
Wietse Venema's Website