Recently, I came across two papers on cross-organization federated identity (authentication, authorization, and audit):

• Identity Federation: The Inside Story (Literally) by Daniel Raskin, Sun product line manager — Explains the roles played by Sun Java System Access Manager and Sun Java System Federation Manager, soon to be merged as Sun Java System Federated Access Manager.
• SAML: The Master Key? by Joab Jackson, Government Computer News — Describes the identity protocol Security Assertion Markup Language and the federated model, with observations from identity experts and adopters.

Informative and insightful, both papers are worth checking out.