Ask HN: Live chat for customer support/sales reccomendations?

We're using a major ticketing system and their live chat is a little flakey (does not take the chat off the site when you go offline). So we're looking around for a standalone alternative and don't mind paying. Anyone recommend a live chat service? Cool features would include: Audio in-your-face ringing if a customer types a msg. Mark a rep offline if the software detects the support rep hasn't done anything on their machine for a while because perhaps they walked away.