Penrose Tiles, of course: http://mathartfun.com/shopsite_sc/store/html/PenroseTiles.html http://mathartfun.com/shopsite_sc/store/html/PenroseTiles.ht... The o

Penrose Tiles, of course: http://mathartfun.com/shopsite_sc/store/html/PenroseTiles.html http://mathartfun.com/shopsite_sc/store/html/PenroseTiles.ht... The online shop for the new Museum of Mathematics in NYC has some of fairly cool stuff, also: https://shop.momath.org https://shop.momath.org