Official Websites
I've been creating Prism (Silverlight slant but most applies to WPF as well) resources:
If you have 5 minutes: 10 Things to Know About Prism
If you have 20 minutes: Prism Basics Video
videos
Intro to Silverlight Prism
Testing/Module Catalog/Unity
Regions (including Region Scope, Region Adapter and Region Context)
Commanding (including creating new commands)
Eventing
podcast interviews with the Prism Team
What is Prism
Modularity in Prism
When to use Prism
View or Presenter First?
Commanding
Event Aggregator
blog posts
10 Things to Know about Silverlight Prism (overview of all resources)
Downloading and Building Prism
I particularly like Brian Lagunas' videos. He has recently been keeping Prism up to date and his videos are mostly in-sync with the latest Prism updates.
brianlagunas.com/category/prism/
Brian Lagunas YouTube Channel
GitHub Prism Library