I've just started reading Secrets and Lies (ISBN 0471253111) by Bruce Schneier, seems to be an excellent book.

I was recommended it from a node I saw here, but I can't find it, I did find the following, and suggest glancing at them too: Re: Bruce Schneier (I little OT); Book recommendation; and Secrets & Lies & Perl.

My 2p.

Update: I've now read this excellent book. In places it's a bit wordy, but overall it's a facinating read, and I would recommend it to anyone even thinking of security. Also see his web site www.counterpane.com for his latest newsletters.