The shoutbox from oggix.com looks ok. Interesting thing is that they even implement a spam prevention method in there! After pressing submit, the system will request the person to key in a number as shown in a display.
And I will not tell you how to break it. No point la. Nice safety feature anyway, that doesn't harm you or use too much energy to key in additional 3 numbers and clicking on submit.
I still prefer my own board.