The Google Charts API supports creating good looking formulas based upon LaTeX input:
Does someone know an online chat service which makes use of that API to display discussed formulas, maybe with the use of editor such as seen in Knol?
I personally use MathIM, which is an online chat room which parses everything between
$$'s in your message as TeX. It's perfect for talking to my friends when I need to use math equations.
It seems to be exactly what you are looking for :)
You can try Pidgin (http://www.pidgin.im/) is an IM client for windows, MacOS and Linux. Then install this pidgin plugin: pidgintext
GmailChatTeX may work for you.