I credit this Melissa & Doug wooden puzzle for teaching both of my kids their United States geography, which is now better than mine. We got a few of these puzzles as gifts when my kids were preschoolers, and they were played with for years (and are still in great condition for resale or handing down).
Amazon's discounted a good selection of Melissa & Doug puzzles for every age, from simple wooden shape puzzles to 500-piece challengers. Great all-purpose gifts for toddlers and preschoolers.
Discount ends May 7, 2010.