http://accelrys.com/products/informatics/cheminformatics/draw/ is the follow up for Isisdraw, free of charge for students, teachers, and researchers in an academic setting. If your willing to pay for a software package then Chembiodraw Ultra works perfectly
ACD/ChemSketch Freeware is a drawing package that allows you to draw chemical structures including organics, organometallics, polymers, and Markush structures. It also includes features such as calculation of molecular properties (e.g., molecular weight, density, molar refractivity etc.)