Recommend a large tarp for sitting around during extended periods of rain while basecamping

Eric, We've been very happy with our Kelty Noah's Tarp 12. We used it in Alaska (the wet part) and it did the job nicely.

Why not get a big blue poly tarp from the hardware store. Very cheap, works great, but heavy.

MSR makes three larger tarps:
1) Vistawing: 2-4 people, 4 lbs
2) Parawing: 4-8 people, 8 lbs
3) Outfitterwing: 6-12 people, 10 lbs.

As you can see these are not light but MSR products are well made and tough.

Cooke Custom Sewing’s Northwoods Dry Fly

Edged with nylon tape, many guy out loops, no grommets to fail, field proven hundreds of miles north of the tree line.

We always carry a "kitchen" tarp on our trips. For your purposes, and for 3 people, you would want something that will withstand the occasional spark from the fire and our unforgiving trees. I'd suggest at least a 7 x 9. If you are not carrying it too far, you may want to have a 70D material. We have a WxTex G2 for kayaking and a silnylon for walking.

Are you going to be below treeline or above treeline/out on the tundra? It will be harder to rig a tarp if you won't have trees, and you may get a lot more wind, and so you may want to get a tougher one or one designed to be free standing or specifically rigged with poles. I have the kelty noah 9, and although I like it, I would also like a regular flat tarp. The cut of the noah is better for hanging of a center line and staking the corners down tight. A square tarp may be easier to rig a-frame style for sitting and cooking (maybe).

I am attracted to the tarps to MEC:
http://www.mec.ca/Products/product_listing.jsp?FOLDER%3C%3Efolder_id=2534374302702975&bmUID=1210298007531

Piragis also has tarps:
http://www.boundarywaterscatalog.com/browse.cfm/2,72.html

You could also go for a Golight Utopia 4 that would also double as your shelter.