I recently received the book 'Real Life Strings' by Sindy P, CZT. It's a book that's full of pictures that are perfect for finding strings based on objects and locations we see all around us. I haven't had a chance to play with it as much as I would like but I'm starting to remedy that.
One of the pictures in the book shows a light fixture as viewed from below. It's the perfect picture for strings for a zendala. I simply put my light box under the page and a round tile and traced the lines easily. Of course you can tangle directly in the book too. So it would be an easy and portable project to work on whenever the mood strikes.
Since this string is all geometric straight lines I challenged myself to use only tangles with straight lines too.
If you are interested in purchasing the book for yourself visit her blog at http://www.sindyp.com/