Some very crude art, using Microsoft Paint...
Tetrahedron (4 triangles)
Hexahedron (i.e., cube) (6 squares)
Octahedron (8 triangles)
Dodecahedron (12 pentagons)
Icosahedron (20 triangles)
...and one of the 13 Archimedean solids:
Icosidodecahedron (20 triangles, 12 pentagons) ("halfway" between the icosahedron and the dodecahedron).
For the other Archimedean solids [such as, e.g. the rhombitruncated icosidodecahedron and other delights], with much better pictures than these, click on the Wikipedia links above.
