Kybalion, Reality transurfing, The illusion of money, The minimalist entrepreneur, Power vs Force, Psycho cybernetics, No self no problem
"Lost Continents" by L. Sprague de Camp (1954). Looks at Atlantis and other lost continents as rhetorical devices in ancient history and philosophy, 20th century pseudoscience/pseudohistory, and science fiction
Anything by Merwin Crawford Young, early Zen Buddhist texts, Anthony Giddens, Peter Berger, the Tao te Ching, Max Weber, Norbert Elias, Nisargadatta Maharaj
By definition such a list is impossible
This would actually just be a list of less well known but still popular books.
Probably 90+% of books published are "obscure" in the sense that they didn't become best sellers and won't be recognized by the average person or likely mentioned in a list like you requested. Most books just don't become popular enough to be well known. Which I think is a tough benchmark.