[database] What are some great online database modeling tools?

Do you mean design as in 'graphic representation of tables' or just plain old 'engineering kind of design'. If it's the latter, use FlameRobin, version 0.9.0 has just been released.

If it's the former, then use DBDesigner. Yup, that uses Java.

Or maybe you meant something more like MS Access. Then Kexi should be right for you.