Recently while trying to find a simple easy to use yet powerful graphical database designer I stumbled across WWW SQL Designer which is a web based JavaScript graphical database designer. I was absolutely amazed by it and it is easily one of the best JavaScript applications I've ever seen, so I decided to host one locally for people to use.
Try it out now in your browser now, WWW SQL Designer hosted at beefsack.com. To see the example database, click 'Save / Load', set 'Server backend' to 'php-mysql' (which is the default), click 'load' and type in 'example'.
When saving and loading you are given the option of storing the data yourself (in the 'Client' box, stored in XML), or the exact same XML can be saved on the beefsack.com server using mysql to store it in a database, or using file to just store it in a file. Just keep in mind that if someone guesses the name you saved under, they can either overwrite your save or load your schema.
For me, the best part is how well drag and drop works and how well the relation lines work. Also, it is compatible with quite a wide range of browsers including IE6 which is pretty incredible. If you like it, be sure to visit the WWW SQL Designer homepage and donate.