This looks neat - I'm thinking of writing a Maypole plugin based on it...
WWW SQL Designer
I've been using this for some time and it is quite cool. It does have a problem if you have quite a complex set of tables, as it doesn't always make it clear with the lines linking the keys which keys it references. Sometimes the lines join other key connections and you have to try and move the boxes around to separate them.
However, in the last schema I created, I used this to create all the basic tables and fields, with the keys linking as best I could, then used The Gimp to redraw the lines or move them
