There aren't any free or Open Source tools available that are any good, AFAIK. There's a schema browser tool for Oracle that's Open Source and uses Gtk and it looks really nice, but it doesn't do any of the fancy stuff you're talking about.
If there *are* any good Open Source tools it would be great to hear about them.
The OpenACS Scheme Browser (which works under Oracle with my repaired ora8.c which I've not gotten around to making available yet) at least lets you find out which tables have foreign keys pointing to your table, triggers on your table, etc. Not much but it does help some...
