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.
WWW SQL Designer - Create database designs, which can be saved/loaded and exported to SQL scripts.
DbDesigner.net - DbDesigner is a web application which allows you to design your database schema without writing SQL.
pgModeler - Open source data modeling tool designed for PostgreSQL. No more DDL commands written by hand. Let pgModeler do the job for you!
DynoBird - Online Database Design Diagram Tool