A wide variety of structure editors (or "drawing editors") are available to help you visualize and search specific chemical structures and reactions. Many of these require Java software, which you can update HERE if needed.
Database providing free browse/search access to around 150,000 ‘small molecule' & 'small to medium-sized' unit cell’ crystal structures. Partial or total database downloading is made possible, using a variety of communication protocols.
Access note: Freely available to the public.