This specification defines the WebFinger protocol, which can be used to discover information about people or other entities on the Internet using standard HTTP methods. WebFinger discovers information for a URI that might not be usable as a locator otherwise, such as account or email URIs.
#webfinger
How Firefox Contacts Auto-Discovery Works
How Firefox Contacts Auto-Discovery Works
Some cool details on real-world discovery for contact details.
Extensible Resource Descriptor (XRD)
Extensible Resource Descriptor (XRD)
“This document defines Extensible Resource Descriptor (XRD), a simple generic format for describing resources.”
hueniverse
Best source for information on a lot of open web and identity technologies.