My kid loves Magformers, plastic shapes with magnets embedded. He plays with them as toys; I appreciate them because they promote spacial reasoning. You can build squares into cubes, triangles into pyramids, and combined shapes into many complex 3D figures.
They are a bit expensive. I got lucky and bought multiple sets from a family off of CraigsList. One of the sets we got has specialized shapes for building dinosaurs. My son enjoys building the dinosaurs but I don’t consider those packs essential. (Magformers offers many other sorts of packs that can get quite expensive.) If I were going to buy sets new, I’d go with a basic starter pack plus perhaps a gear pack (paid links).