You can create entity-relationship diagrams (ERD) with Gliffy. ERDs are useful for describing data and the rules that determine how entities and attributes interact with each other. An ERD is hugely important in database design and should be the first thing you draw when contemplating database architecture. (For a more in-depth look as well as a description of commonly used ERD symbols and their meaning, see this blog article).
To help you create them, when you create a new diagram, you can choose from several Entity Relationship - ERD templates.
And, several Software Design shape libraries offer shapes like doors and furniture.
For more information, see Entity-relationship arrows.