To
davidwilsoon
what about 123 Web Messenger. It is an IM chat software. which enables one to one private chat among users:
http://www.123flashchat.com/web-messenger-chat.html
And according your requirement, what about the Facebook Like Chat Bar:
http://www.123flashchat.com/web-messenger-chat.html
You could see it at the bottom of the tool bar. Please check it now.
Though it is not at the top, but i think it is suitable for your requirement.