We have made our own live chat engine that works with IRC, thats really nice because we all can see the chat. I think make your own system is the best opinion because you can build for your own requirements.
Yes, that's true but what about live visitor monitoring to see who is on your site and where they are coming from 'LIVE'?
That's really why I live the live chat features and we are currently using Comm100 live chat feature.
We also custom designed an IRC based system as well using a web chat interface and mIRC clients on our staff computers.