Monitoring the activities of the Internet Engineering Task Force (IETF) is a good way to keep up with emerging standards related to VPNs. IPSec, for instance, is an IETF working group attempting to create a standard for secure IP communication, which can be used in VPNs. See http://www.ietf.cnri.reston.va.us/1id-abstracts.html for a draft index.
Remember that most of these drafts haven’t been implemented outside of experimental environments yet, so look to this site to provide you with information on “up-and-coming” Internet technologies. RFCs are informational documents on technologies that may already be in place. An index of actual RFCs can be found at http://www.ietf.org/rfc.html.