I would hope most security geeks are aware of the Kryptos Sculpture located at the CIA's Langley headquarters. Artist Jim Sanborn unveiled this cryptographic sculpture in 1990.
It took until 1998 until someone decrypted 3 of the 4 panels. Analyst David Stein did so, and he wrote a paper on it. It was published in the CIA’s classified journal Studies in Intelligence. Note that ONE panel is still unsolved.
Thanks to THIS ARTICLE at Wired.com, it seems that the National Security Archives has made this now unclassified work available. You can read it HERE.