Zentangle has added their stamp of approval an some of the supplies I've listed below but I tend to use the non-official aka less expensive versions more.
Zentangle Web Resources - Part 2
Zentangles for Mindfulness
Lets Color! Coloring Books for Grown-Ups
Free Coloring book pages for adults - Coloring Book Addict
Zentangle Art for Kids Project
What to bring on vacation: travel light with your Zentangle
The Best Zentangle using Posca pens
How to Get Started as a Zentangle Beginner – Tangle List
Best Markers for Adult Coloring Books that don't bleed through the paper
Zentangle The Meditative Art — Art Supplies Suggestions and More
How to Get Started as a Zentangle Beginner – Tangle List
10 Best Zentangle Sites on the Web