Just some links that I use on a regular basis.
Windows Identity Foundation Simplifies User Access for Developers - Home page
Windows Identity Foundation - MSDN Library
Identity Developer Training Kit - Read the System requirements
The Id Element - Identity and Access Management videos
Active Directory Federation Services 2.0 - Home page
AD FS 2.0 Step-by-Step and How To Guides - Includes a number of federation guides e.g. PingFederate, Oracle Identity Federation
Vibro.NET - Vittorio Bertocci's blog
Steve on Security blog - Good code examples
dominick baier on .net, security and other stuff - The man behind Thinktecture and StarterSTS
Claims-Based Identity Blog - Some good examples of federation with other systems
Eugenio Pace - Examples, architecture and interoperability
Matias Woloski - The guy behind the OpenId bridge
Travis Nielsen - Federation and SharePoint 2010
Alik Levin - Lots of Windows Azure AppFabric Access Control Service (ACS)
Steve Peschka - Special emphasis on Sharepoint 2010
Claims based access platform (CBA), code-named Geneva - Worth keeping an eye on
Of course, Stackoverflow:
Essentially collections of links - like this one!
TechNet Wiki Windows Identity Foundation (WIF) and Azure AppFabric Access Control Service (ACS) Survival Guide
Windows Identity Foundation (WIF) Fast Track
Windows Identity Foundation (WIF) SDK Help Overhaul
Windows Identity Foundation (WIF) Questions and Answers
StarterSTS - StarterSTS is a compact, easy to use security token service that is completely based on the ASP.NET provider infrastructure. It is built using the Windows Identity Foundation and supports WS-Federation., WS-Trust, REST, OpenId and Information Cards.
StarterRP - A relying party for StarterSTS
SelfSTS - SelfSTS is a simple utility which exposes a minimal WS-Federation STS endpoint. SelfSTS can be used as a test STS when developing web sites secured with Windows Identity Foundation. Allows you to quickly generate combinations of claims.
SelfSSL7 - Self signing certificates for IIS7. Generates and stores them. Refer my blog entry WIF : Self signed certificates for instructions.
Protocol bridge claims provider - An implementation of a bridge that talks WS-Federation and SAML tokens on one side and OpenID, OAuth or any other protocol on the identity provider side using Windows Identity Foundation.
Fiddler Inspector for Federation Messages - An inspector for typical federation messages for WS-Federation. Also has support for SAML 2.0P request / response messages.
Security Token Visualizer Control - A simple ASP.NET server control which displays in a compact layout useful information about claims-based identity in a web site secured with Windows Identity Foundation. Just get it!
A Guide to Claims–based Identity and Access Control - Just read it - cover to cover - twice!. By Eugenio Pace, Dominick Baier, Vittorio Bertocci, Keith Brown, and Matias Woloski. See their blogs above.