Mercer Street Books, Greenwich Village, Manhattan
Mercer Street Books has been in business for 25 years! It's a mostly used and rare bookstore though they do carry some new books as well. They carry books in just about every genre and apparently all the clerks are writers as well. So they know something about books! They buy and sell and they carry vinyl records as well.
So it's a bit of chaotic mess. But most of the books are in sections that make sense. I have found books there they I don't see in other bookstores and their collection is impressive. They are located next to the NYU campus and just next to Soho. They are in an area that is going through much gentrification. I do hope that they will be there for another 25 years!
Mercer Street Books, 206 Mercer Street