[These are the lightest tarps each popular company offers excluding Zpacks, where I’ve opted to use their hammock style tarp instead. All info is based on information from each companies website. Feel free to add anything I've missed.]

Company: Zpacks
Tarp Name: Hammock Tarp
Style: Hexagon
Material: .51 oz Cuben Fiber
Dimensions: 11’ X 8.5’ X 7’
Weight: 5.1oz
Price: $235
Website: www.zpacks.com/shelter/tarps.shtml
Company: Hennessy Hammocks
Tarp Name: 30D Silnylon Rainfly
Style: Parallelogram
Material: 1.1 ounce 30D Silicone Nylon
Long side = 92"
Short side = 65"
Long diagonal = 122"
Short diagonal = 105"
Weight: 8.4oz
Price: $60
Website: www.hennessyhammock.com
Company: Mountain Laurel Designs
Tarp Name: UL Hammock Tarp
Style: Diamond
Material: .97 oz sq/yd silicone Spintex09 EXP
126" Long Diagonal
102" Short Diagonal
98" Long side
59" Short side
Weight: 4.7 oz
Price: $90
Website: http://www.mountainlaureldesigns.com...roducts_id=149
Company: Warbonnet
Tarp Name: Asym-Diamond
Style: Diamond (Offset corners)
Material: 1.3 oz Silnylon
Dimensions: 132” X 100”
Weight: 7.5 oz
Price: $75
Website: www.warbonnetoutdoors.com/tarps.php
Company: Outdoor Equipment Supplier
Tarp Name: MacCat Micro
Style: Hexagon
Material: .95 oz SpinnUL
Dimensions: 120” X 60”
Weight: 5.6 oz (With stuff sack)
Price: $125
Website: http://www.outdoorequipmentsupplier....ccat_tarps.php

(I know I skipped some bigger companies, but for the most part it was due to the lack of a UL tarp.)