A new drop of the official SharePoint Guidance. It now covers SharePoint 2010 and further expands on the SharePoint solution architectural decisions and implementation guidelines.
After some time using Web Client Software Factory (WCSF) guidance from Microsoft p&p team, they are now coming with a new version of web client guidance, oriented to ASP.NET with jQuery, AJAX and even ASP.NET MVC. Excellent read, even in the present rough form.
A guide to Claims-based Identity and Access Control, with a downloadable book in PDF format. It’s invaluable in understanding the new Windows Identity Framework (former Geneva Framework) and SharePoint 2010 claims-based authentication.
Web Service Security Guidance for WCF, available as an online book and as a PDF file. I admit that WCF is a huge step forward in distributed applications but the security implications are too important to be left unattended. After reading this guide I had clearer image of all those pesky web.config WCF tags and their effect. Priceless when you are debugging cross-domain WCF calls :-)