“Data Modeler” is a free tool to create Microsoft SQL Server databases.
If you are trying to design a databse correctly and this is one of the good database design GUI.
Some of the popular features of Data Modeler are
Real-time model validation
Table data synchronization
Drag ‘n’ drop foreign key creation
Automatic query script creation
Automatic relationship line placement
Object-level DDL previews
Update/delete foreign key automation
Customizable fonts and colors
For more details, Please refer http://sourceforge.net/projects/sqldatamodeler/
You can download it from here – http://sourceforge.net/projects/sqldatamodeler/files/latest/download