Active Directory Federation Services Tech Center
Like Steve this is one of the things that I get asked about frequently and this page has some great resources –
https://technet2.microsoft.com/windowsserver/en/technologies/featured/adfs/default.mspx
This page is designed to help you connect with resources and documentation for Active Directory Federation Services (ADFS) in Windows Server 2003 R2. ADFS extends the ability to use single-sign-on (SSO) functionality that is available within a single security or enterprise boundary to Internet-facing applications so that your customers, partners, and suppliers can have a streamlined user experience while accessing Web-based applications.