A lot of people don't know this but I first heard about memory techniques through the world of mental calculation. Growing up studying Physics and Mathematics, I was always reading books about the top guys and occasionally a prodigious mental calculator. Art Benjamin is our modern day mental calculator. He has been teaching Math at Harvey Mudd College for years, but his TED talk in 2005 really put him on the map. I believe that talk is still one of the top 20 most-viewed TED talks of all time (here: https://www.ted.com/talks/arthur_benjamin_does_mathemagic?language=en). In it, he does some amazing "mathemagic" (which is really just some seriously impressive mental calculation; no magic there) that wows the crowd. I've also read his Secrets of Mental Math book at least a dozen times.
He's awesome and a huge idol of mine. I can't believe I actually got to sit and chat with him. But anyways, have a watch/listen and learn about one of the COOLEST minds I know.