I found a combination of the Ultra VNC repeater and Ultra VNC SingleClick to be wonderful. It works like GoToMyPC in that you don't care about the client's firewall. It can be a little laggy at times, but it works well. Ultra VNC is also free, no matter how many clients you set up. It's the best kept secret out there.

http://ultravnc.sourceforge.net/

To set it up:
- Install the repeater on a machine that will be visible to the internet. Right-click the repeater tray icon and Configure the Accept port to 5901, and the listen port to 5501. Enable modes I and II. Restrict access to server port 0. Save, restart the repeater.
- Forward those ports on your router to that machine.
- Download the SingleClick package http://ultravnc.sourceforge.net/addons/singleclick.html
- Edit the helpdesk.txt. You put in the URL/IP address of your repeater server, and add in a list of your support staff. You give each one of your support staff an ID number in this file.
- Make a zip file like support.zip with the helpdesk.txt in it.
- Run the SingleClick exe builder on the Ultra VNC website. This will upload your support.zip and gives you back a customized support.exe
- Put this support.exe on your web site so that clients can download it.
- Install the Ultra VNC package on your own system(s) so that you have access to the viewer.
- Make a shortcut for your desktop(s) to run the VNC viewer with parameters so that it contacts your repeater and gives it your individual ID number.

Now you just have the client download support.exe and run it. They can select the name of the support staff to be connected to them. You run your viewer, and bingo you get connected! You have full remote control with file transfer. No more messing with ports on a clients system, no more PCAnywhere!

I am not part of the UltraVNC group, but I would be glad to help anyone that wants to try it.