I've been using PHPLiveSupport from
http://www.phplivesupport.com/ on my site for quite some time for the chat functionality. Very, very easy to integrate, and I get a ton of customers online using it. I forget the fee, but the software is like $100 one-time-fee, so it's not hosted, and you don't pay a recurring fee.
If you'd like to see a live example, you can visit my site at
www.aostuff.com.
Take care,
Nick