jQuery UI Chatbox Plugin. Souce code This is a jQuery UI plugin I wrote as part of a data collection tool for the social network analysis project I've been working on, in which this plugin serves as the front end of a simple Comet chat server.
It is a pure UI plugin so you can easily plug it into whatever communication protocol of your choice, some may find this useful. Socket.IO: the cross-browser WebSocket for realtime apps. Frug/AJAX-Chat. Blueimp's AJAX Chat. Endtwist/AjaxIM.