Eu recomendo o Teamviewer , já que é gratuito (para uso não comercial) e permite que você envie convites personalizados
Algumas características interessantes
Works behind firewalls
The major difficulties in using remote
control software are firewalls and
blocked ports, as well as NAT routing
for local IP addresses. If you use
TeamViewer you don't have to worry
about firewalls: TeamViewer will find
a route to your partner.
Browser based access
On the road and need to control a
remote computer? Why don't you use
TeamViewer Web Connector? The purely
html and flash based solution can be
used from nearly any browser and
operating system.
Remote support without installation
With TeamViewer you can remotely
control any PC anywhere on the
Internet. No installation is required,
just run the application on both sides
and connect - even through tight
firewalls.