In my post on implementing an in-memory encryption scheme to protect sensitive information, I referenced a mitigation strategy called a Boojum. It is described by Bruce Schneier, Niels Ferguson and Tadayoshi Kohno in their book, Cryptography Engineering: Design Principles and Practical Applications.
A number of people asked me about the mechanisms of the attack and the scheme, so I am including the relevant parts here. It is an excellent resource and I recommend that you go and buy it.
-  Jurjen Bos. Booting problems with the JEC computer. Personal communications, 1983. [Page 125]
-  Lewis Carroll. The Hunting of the Snark: An Agony, in Eight Fits. Macmillan and Co., London, 1876. [Page 126]
-  Giovanni Di Crescenzo, Niels Ferguson, Russel Impagliazzo, and Markus Jakobsson. How to Forget a Secret. In Christoph Meinel and Sophie Tison, editors, STACS 99, volume 1563 of Lecture Notes in Computer Science, pages 500-509. Springer-Verlag, 1999.
-  Peter Gutmann. Secure Deletion of Data from Magnetic and Solid-State Memory. In USENIX Security Symposium Proceedings, 1996. Available from http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html.
-  J. Alex Halderman, Seth D. Schoen, Nadia Heninger, William Clarkson, William Paul, Joseph A. Calandrino, Ariel J. Feldman, Jacob Appelbaum, and Edward W. Felten. Lest We Remember: Cold Boot Attacks on Encryption Keys. In USENIX Security Symposium Proceedings, pages 45-60, 2008.