Great Articles and Videos on Authentication

Videos -

Claims Quick Walk-Through by SharePoint Sideshow
http://channel9.msdn.com/Shows/SharePointSideshow/Understanding-SharePoint-2010-Claims-Based-Security

Great Claims Overview with Program Manager from Microsoft
http://channel9.msdn.com/shows/Identity/Sharepoint-2010-and-Claims-Based-Identity/

Convert from Classic to Claims
http://sharepointgalaxy.blogspot.com/2011/10/convert-classic-to-claims.html

MSDN - Identity Team Blog
2010 http://blogs.msdn.com/b/spidentity/

More Great Articles
TechNet Article on Authentication
2010 http://technet.microsoft.com/en-us/library/cc288475(v=office.14).aspx

ADFS
http://dangermouseonsharepoint.wordpress.com/2011/11/10/sharepoint-2010-and-ad-fs-part-1/

SAML - Configure authentication using a SAML security token (SharePoint Server 2010)
2010 http://technet.microsoft.com/en-us/library/ff607753.aspx

FBA – Configure forms-based authentication for claims
2013 http://technet.microsoft.com/en-us/library/ee806890(v=office.15).aspx
2010 http://technet.microsoft.com/en-us/library/ee806890(v=office.14).aspx
FBA - Forms Authentication in SharePoint Products and Technologies (Part 1): Introduction
http://msdn.microsoft.com/en-us/library/bb975136(v=office.12).aspx

MSDN on Authentication
http://msdn.microsoft.com/en-us/library/ff359108.aspx

Security and Authentication for SharePoint Server 2010
http://technet.microsoft.com/en-us/sharepoint/ff601872.aspx

SharePoint Security and Permission System Overview
http://www.sharepointblues.com/2010/09/01/sharepoint-security-and-permission-system-overview/

SharePoint Security - SharePoint Authentication Part 1
http://www.sharepointmonitor.com/2011/02/sharepoint-security-authentication/

Good overview of authentication
http://technet.microsoft.com/en-us/library/cc262350.aspx

Double Authentication http/https issues
http://technet.microsoft.com/en-us/library/cc995228.aspx

OLD
http://sharepointgalaxy.blogspot.com/2011/10/authenication-issues.html
http://sharepointgalaxy.blogspot.com/2011/09/sharepoint-authentication.html
MOSS Articles that are still a good read
http://geekswithblogs.net/SoYouKnow/archive/2009/03/11/everything-i-know-about-sharepoint-fba.aspx
http://technet.microsoft.com/en-us/library/cc288081(office.12).aspx
MSDN Two part series on MOSS
http://msdn.microsoft.com/en-us/library/bb975136(v=office.12).aspx
http://msdn.microsoft.com/en-us/library/bb975135(v=office.12).aspx