Some of the new Crafter's Workshop Templates seem to make prefect canvases for Zentangling. You can draw around the edges of the template design or use a spray ink like Fireworks! from Tsukineko to create a template of color. Add a few stamped images and you've got a tangled masterpiece.
What is Zentangle? My definition, in a nutshell is that it is semi-scripted doodling. You can come as you are, with lots of ideas or no ideas and still create a masterpiece that's all your own. The people who coined the term "Zentangle" suggest using it as a sort of meditation. They even certify instructors to make sure it is being taught properly. Me? I just doodle, borrow some patterns and if I find a state of Zen along the way, great. I am a totally unlicensed doodler. That's the great thing you can take it as seriously as you want. We carry these great inexpensive books about Zentangle, written by a certified Zentangle instructor if you want to know all there is to know about Zentangle. They also have great patterns!