Chemical+Database+Online

ChemID http://chem.sis.nlm.nih.gov/chemidplus/

This website also has a nice tool or applet for drawing chemical structures: MarvinSketch

Marvin chemical drawing software can also be found here (a download link on the ChemAxon website) https://www.chemaxon.com/download.php?d=/data/download/marvin/5.11.5/marvinbeans-5.11.5-windows.exe