Apple's Remote Desktop client is the only VNC server I've found that could display both of my displays (G4 with dual video output, connected to two 1600x1200 monitors, for an effective 3200x1200 sized desktop). However, ARD client is also the least configurable VNC server that I have found.
One common issue is not being able to change the port it runs on (default is 5900) ... simply put, I have not seen a true way to do this within the client itself. I wanted to move to a non-standard port (partly for security by obscurity, though I realize that's not real security). Other folks have the issue of wanting to connect to multiple Macs inside the same network.
A real hack that came to mind is this: I have an Airport Extreme router (though almost any router should suffice). From outside the local network, you can configure the router to port forward, as shown in this Apple article.
Use the Port Mapping Setup Assistant to map the following:
Port 5906 on the outside (Public) can be mapped to (Private) port 5900 on machine 10.0.1.2. Hit Continue, then add additional mappings as needed, ie:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080107061618164