I'm looking for a service (happy to pay) that will provide Facebook style chat to users of my website. I'd expect it to work somewhat like Disqus but probably require a bit more work to implement user account integration.
Another one you can try is the open source Ajax IM. What you have to ask yourself is how many users will you have and can you handle the traffic. Especially when you want to have the chat server on your system. Else it would be better if you take an external service.
Try RumbleTalk HTML5 JS widget. The main benefit is that you can stay connected also from your mobile.
The best of its kind