Here's a simple pattern that pops nicely to life with a little shading.
Note that in the example art below, I am using several patterns from members of my new flickr group, Freehand Doodle Patterns. I started it so that people could post their tangle patterns in a common place making it easier for you, the hopelessly addicted zentangle enthusiast, to find that pattern you saw, but can't remember where. Lol! Or am I just projecting myself onto everyone else?