NIST published their Critical Infrastructure Protection guidelines and I also noted the National Information Assurance Program (NIAP) Process Control Security Requirements Forum (PCSRF). Wish I had these references about four years ago. This is an especially interesting paper, which I think was done for the PCSRF and ISO/IEC 15408:

http://www.isd.mel.nist.gov/documents/falco/ITSecurityProcess.pdf

The Gas Technology Institute/American Gas Association Encryption page also has some good pointers and here’s the Department of Energy (DoE) guide to CyberSecurity.