In reply to slawosz:
We use 2 Mountain Equipment Aurora's. We got the left zip on one and a right on the other so we can turn them into a double bag. They are what I would call a synthetic workhorse, extremely well made and showing no signs of wear after 3 years of heavy use van camping.
You can often get deals on Mountain Hardwear bags at either Rock + Run or Sport Pursuit. A friend of mine uses one of theirs and loves it.