ABChat - free chat resource for webmasters
This service provides a full featured and easy-to-cofigure remotelly hosted chatrooms for websites. No special downloads are required for end-users.

Chipmunk Free Chat Script
Chipmunk Chatbox is a simple chatbox written completely with PHP and MYSQL, admins can specify if guests can chat or not. Version 1.1 also shows list of registered users within last 15 minutes.

LiveSiteManager
LiveSiteManager is a simple and affordable solution for adding live chat to your web site, email, banner ads, and auction/calssified listings. With it, you can easily deliver the right information, to the right customers, at the right time through an easy-to-use chat interface. Packages start at $39 per month.

ParaChat
Power your web site with a Java powered real-time chat. A range of packages are available, with the most basic service being free

WebsiteAlive
AliveChat is a free live chat software for web sites interested in providing live help and live support to visitors for sales and customer service chats.