ChemSpider

ChemSpider is a free access service providing a structure centric
community for chemists. Providing access to millions of chemical
structures and integration to a multitude of other online services,
ChemSpider is the richest single source of structure-based chemistry
information.

My opinion: again a new player into the Chemistry area. Its intuitive
interface and associated links to commercial providers of compounds
could be appreciated by PubChem or SciFinder users.

http://www.chemspider.com/