Netbeans 6.0b1 comes already with a built-in SQL-Editor. However it also containts the Visual Web Package extensions. The usage is easy - go to tab "services", connect to a database and choose a table. From the context menu choose "Design Query", instead of e.g. View Data.
The tables are visualized - you can drop other tables into the view. Event the links between the tables are visualized. I use this feature to understand legacy databases - however it was originally intended to design queries :-).
This feature is not really new, however it comes with Netbeans 6.0b1. The visual capabilities are based on the visual library (http://graph.netbeans.org/) - so you can use this framework for standalone projects as well.