Okay, I got a nice list of [seemingly] good choices here.
http://www.freejavachat.com/index.html
Free, ad supported, not moderated.
http://www.sigmachat.com/services.html
Pay by year service at 75 USD per year, no set up charge, moderated.
(PRO setup)
http://chat-forum.com/freechat/index.htm
Free, ad supported, moderated.
http://chat-forum.com/prochat/index.htm
Pay by year service at 30 USD per year, with a one time setup fee of 200 USD(IIRC). Moderated, able to have multiple rooms.
http://www.visopsys.org/andy/babylon/download.html
Free, no ads, moderated, able to do whiteboard.
This one seems like it'd be the best choice, but it's only a beta, and I didn't test it out yet, so I don't know if it's really buggy or not.
I am also not sure if it's only the owner of the chat or everyone who wants to chat that has to download it...
So anyway, there's your list.