MySQL Workbench is a unified visual tool for database architects, developers, and DBAs. MySQL Workbench provides data modeling, SQL development, and comprehensive administration tools for server configuration, user administration, and much more.
Free visual data modeling inspection tool for most popular one-way reverse-engineered relational databases. With a generic graphical interface, and auto-generated detailed, structural, relationships, simple, graph or topological models.
Visual Alchemist is an open source web-based database diagramming and automation tool. Visual Alchemist is a pure html app, so you can simply download the source and host it (with index.html as default).