Excellent security resources I've mentioned at InfoSec, the Technical (TechNet & MSDN) Roadshow and at TechEd / IT Forum
Spurred on by Anil John's (** Edited to correct my earlier typo - sorry Anil **) post (referred to here) here's my list of key security resources - it's not meant to be exhaustive!
Prescriptive Guidance,
More Prescriptive Guidance
How MSFT implement a secure infrastructure
Online recordings of top infrastructure speakers
Network Segmentation via IPsec