Nylon tarps seem the best bang for the buck - REI has a standard one, so does Campmor, 8x10 or 9x10 seems a good size to get pulled out and used alot (~ 1 lb). My current tarp is the REI brand, but that's because I got it really cheap at one of REI's .83 sales a while back. Kelty makes a really nice tarp, don't know the weight or sizes but I seem to recall they are blue and white and they have alot of grommets along the side for tying down (ck REI website). Silnylon is even better, but pricey. The nylon tarp isn't too heavy to hike in a day or two.