The ACT Hexaflex
I love this very comprehensive diagram from Nesh Nikolic. The Hexaflex is a commonly used diagram to show the 6 Core Principles of Acceptance and Commitment Therapy. What I like about this one is that it has a clear description of each of the principles.
Each event of my Mindfulness Outdoors Group and Mindfulness Outdoor Retreat (coming soon) explores at least one of these principles.