For a unit on folktales I assembled a list of candidates on a world map. You can view this map here:
Each location on the map includes a book summary and a link to learn more. Use this map for your own reference, or use google maps to create one like it. As we cover each folktale: we'll add a pushpin to our own world map and talk a little bit about where each story is from. This will help introduce students to different countries and continents over the course of the semester.
(Also this helped us make sure our book selection was spaced out geographically!)
This map points to dozens of books on Amazon, but also a few dozen stories that are part of the public domain. Since they are free, the public domain stories won't come with highly engaging illustrations -- but you can pick a few and make illustrating them part of a subsequent craft. Also a few stories in the public domain are available on librivox as audiobooks.
This is just a buffet of choices from which you can derive your unit plan.