MySQL Workbench - MySQL Workbench is a unified visual tool for database architects, developers, and DBAs.
Navicat Data Modeler - Navicat Data Modeler allows users to create a conceptual model from an existing database and edit the structure of the database easily.
SQL Developer Data Modeler - Oracle SQL Developer Data Modeler is a free graphical tool that simplifies data modeling tasks.
Model Xtractor - Universal Data Model Inspection Tool
DbDesigner.net - DbDesigner is a web application which allows you to design your database schema without writing SQL.
WWW SQL Designer - Create database designs, which can be saved/loaded and exported to SQL scripts.