A long time ago (in university) I read this lock picking guide.
I recently re-read Surely You're Joking, Mr. Feynman which contains (among other things) memoirs of how Richard Feynman cracked safes at Los Alamos during WWII. (The safes in question weren't very secure.)
And now I read Safecracking for the Computer Scientist by Matt Blaze, an excellent examination of safe security and comparisons to information security.
Fascinating stuff. Now where can I get a safe to play with?