First thought was iChat, but I already had Colloquy and Adium running and last time I tried iChat it wouldn't connect to the AIM server.
Next, I remembered getting an email from LogMeIn about a new service for free screen sharing. I went to the LogMeIn site and found Join.me and clicked on it. It started up Java, and I downloaded some Java code and a small tool bar appeared at the top of my screen. It didn't seem to take even a minute. I pasted the link provided in the tool bar into my Colloquy chat window and my colleague clicked on it.
He didn't need to down load anything. The Java code runs on my system, pushes my screen data to the server and he got a Flash driven experience, complete with zooming and screen resizing right away. We never had any lag, though he was working from home quite a few states away.
Fast, Easy, Free, Unobtrusive, Highly Functional: Join.me is a winner