The Ben-Ben stones were 'real', in as far as they were the ceremonial and practical capstones of the pyramids. I heard Dr. Zahi Hawass talk, last evening (January 20, 1998 at the Dept of Agriculture, Jefferson Auditorium) at a Smithsonian Institution Associates event, about discovering a BenBen capstone near the Great Pyramid at Giza. 
 

pages with references to BenBen Stones: 

From ancient Egyptian myth, the hill which was the first land to rise from the waters.