Not only a great chat system, but also a great interface enhancement
I bought CometChat for the Facebook-style chat features, which integrates beautifully with JomSocial to show you your online JomSocial friends in a chat bar pegged to the bottom of the browser window. And it does that job so well, that if it did nothing else, I would have been delighted with my purchase. But no, it opens so many more possibilities to enhancing the user interface of your site. Just by making some simple modifications to the config file, you can quickly add your own custom toolbar icons for either shortcuts to your commonly-used content, or for gorgeous toggled window displays of information that becomes available on every page. I have links to my homepage, user's profiles page, new forum posts and even badged notifications of new private messages.
The user interface is simply gorgeous, and my visitors love it.