Molecular Assembly Program
You  might want to try BioVia's (formerly Accelrys) Discovery Studio Visualizer. This is free software and the "gateway drug" to their sophisticated suite of molecular modeling and chem/bio informatics software. It is a step above the various drawing programs out there and lets the user generate realistic 3-D models of an infinite variety of chemical structures. http://accelrys.com/products/discovery-studio/visualization-download.php