The Oztrail Ultra rig tarps are good quality, heaps of eyes and pretty cheap. Avoid canvass as the weight of them when wet it staggering!

Make sure you have a pole for EVERY eyelet for maximum strength, if you are using a long rectangle tarp you can put two spreaders across the short side instead of one long one down them middle, this also makes it easier to keep the tarp flat without using an A shape in the tarp.