Awesome Database Design Tool: wwwsqldesigner
If you want to use it, it helps to have a web server to install it on, but it’s not mandatory. If you have a web server with a database server, you get the added bonus of being able to save your designs to the database using PHP and MySQL. If you don’t have a database server and/or web server, you can save the design as an xml file, and load it again super easily.
It’s hosted over at Google Code: http://code.google.com/p/wwwsqldesigner/