Free and open source database design software
DBDesigner 4
“DBDesigner 4 is a visual database design system that integrates database design, modeling, creation and maintenance into a single, seamless environment.” Looks very robust. One of the few tools that supports reverse engineering.
MySQL Workbench
“MySQL Workbench is a cross-platform, visual database design tool developed by MySQL. It is the highly anticipated successor application of the [...]