I never thought about it being a "zen" thing but I've done this sort of doodling since I was in middle school and come to think of it, I'd do it when I was nervous, upset, or overwhelmed.
zentangle patterns - this is all I'm going to be doing in class now.
Open Seed Arts: Koolapopper/Footlites Fun
Zentangle Patterns & Ideas
Variations of Leaves and Shapes~zentangle
nia variatiions by sheridanwild, via Flickr
Zentangle Pattern Gallery | Zentangle Patterns 2 - a gallery on Flickr
Petales de Fleurs (Freehand Doodle Patterns)
Christmas Zentangle Patterns
ZENTANGLE PATTERNS noncat 8 | Flickr - Photo Sharing!