I've found that those plastic bags from the grocery store work pretty good
Seriously, I've been using a
BAGMASTER for a couple years now. Relatively inexpensive, pretty durable and lots of different sizes to choose from.
Blackhawk is probably considered better, but I think for average range use BM should be just fine. I myself have their Pro-Shooter's Large model. A cool trick that I did was I bought their 8 magazine pouch and it fits perfectly inside next to the pistol pouches. I keep the flaps folded back so I have this easy access 8 magazine holder right there in the bag.
LL