I have a need to do some UML and ERD diagrams for class and the lack of any really good tools with demos or that are out-and-out free for educational use is kind of a pain in the ass. I've used ...

I can't find the free ERD tool that I used years ago when I was dabbling in database stuff. It wasn't great but it was enough for my needs. Probably would be too simple for any real use though.