The best tarp for camping is the Warbonnet Superfly, made by a guy named Brandon! It's primarily used for hammock camping in severe weather, but would be great for all you "ground dwellers". Here's a link:
http://www.warbonnetoutdoors.net/

I can't say enough good things about this guy and his products. He made hammocks so good, Tom Hennessy tried to sue him last year. I am very pleased with my Superfly and will use it year round!

BF
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Hammockers aren't stuck up, they're just above it all.