As of October 2015, some good folding shopping carts are Sandusky's model FSC4021, the Polder Superlight Shopping Cart and the Two-Wheel Folding Shopping Cart from Faucet Queen. All average at least 4.2 out of five stars on retailers' websites.
Sandusky's cart holds 110 pounds and comes with a protective liner that keeps items from shifting. Positive reviews at Amazon.com say that the cart is sturdy and easy to assemble. The Polder cart is lightweight and holds up to 30 pounds. Reviewers at Home Depot's site state that it arrives already assembled and is easy to fold.
Faucet Queen's cart has a fold-down shelf to hold lighter items. Reviewers at Walmart's website mention that the cart fits together easily without tools and is a good value.