I, like Fiddleback, use parachute cord. It is also known as 550 cord, I think because it can withstand 550 lbs of weight. Go figure. It is available in 100' packages from outdoor/surplus stores. 1000' spools go on ebay for about $30-$40. It comes in many different colors from the standard military OD green, coyote brown to blue and purple if that is what you are after. I have found it to have endless uses such as pack repairs, guy lines, bear bag hanging cord, arts and crafts projects. It makes great shoe laces. It has nylon type filaments encased by a woven tube of nylon making for a smooth cord. The ends fuse nicely with a flame.

By the way I do not sell 550 cord. Just a satisfied consumer. Here is a picture that illustrates what it looks like.
http://i6.ebayimg.com/05/i/000/b5/ba/dae0_1.JPG