I've got two Wald folding baskets on my errand/utility bike. They're heavy, but I like them a lot. One of those "green bags" - the cloth grocery bags - fits in each basket, and allows you to secure something else to the rack as well, so you can carry a pretty respectable load of stuff. I can do the grocery shopping for a family of 3 with that bike, going to the store twice a week.

The folding feature is nice when I'm not carrying anything, or when I only have stuff on one side.