I've used a number of different types of dry sacks, and these, along with the Sea to Summit eVent Dry Sacks, are among my favorites.
The great thing about an eVent dry sack is that you can squeeze the air out of the sack after you've rolled and closed the top. So for bulky, compressible items like down jackets or sleeping bags, you can reduce the space taken up in your pack.
I've also used sack
This review was written in the old system and had content requirements that are different than reviews written today.