Interactive Platonic Solids on NCTM Illuminations Site. Note the questions for kids (and you) in the table.
MathsNet Interactive
Geometry: Platonic solids Nets.
Use the display and the slider to see how shapes up made up from
their nets.
Definition of Nets from MathWorld
Archimedean Solids from MathWorld
Lots of Java interactive polyhedra including the Buckyball and the Rhombic Dodecahedron
Cutting the Cube from Annenberg/CPM Learner.org