Teacher Produced
Teachers can put together stacks on a content topic for students to use in their study. The best I saw was at James Logan High School. Details.
Student Produced
Students can create stacks on a topic they are studying. The most surprising I saw was at Town School where the students worked without the teacher even being there! Details.
Another at Town School involves creating a library of book reviews for other students to access to help them in choosing free reading books. Details.
And finally, a teacher in Michigan has the students create stacks as sequels for books they've just finished reading. Details.