Shamefully, many online resources are not maintained and so the information is lost as time passes. While these are currently links to external sites, my intention is mirror these resources here for longevity purposes.
General
The Medieval Tailor's Assistant
Medieval Clothing Articles
Historical Costume Patterns
Viking
Simple Viking Clothing for Men
Viking Tunic Construction
Cloaks
A simple semi-circle cloak
Comprehensive instructions for various cloak designs