I am not a big fan of Adobe Flash, but this project is brilliant!! It allows you to create dynamic graphs for a website and unlike Java based applets, it loads quickly and without hassel, even on my Linux machine (Java applets currently not working for me). Go check out the demo at: http://flare.prefuse.org/demo/
Flare is great indeed. Allows you to create fancy apps.
Another great visualization site is http://www.drasticdata.nl
Have a look at it, they have some nice examples.