Risk of Remote control software to your corporate network (webex,
gotomypc, logmein, etc) - Require a detailed description of the threat
these 'tunneling' applications pose to a network and any ideas or
recommendations about how to protect or block this threat from
entering an organisations networks

It really depends on how your network is configured, the remote
tunneling programs you listed generally use a port 80 tunnel which is
a little difficult to block as you would need specific information on
the connection to block it. However if it is through a service you
could use a program like peerguardian and set up a special block list
to block the ip addresses of the services so people cannot connect to
the serivice. You could also run all your http traffic through a proxy
server, as long as it is configured correctly and port 443 is not
allowed to connect directly to another computer, you could filter
access to tunneling services and prevent their access. Also many of
the services depend on ActiveX controls or Java scripts, you can
prevent almost any browser from connecting to certain url's to prevent
these scripts the services require, for instance, if the systems you
use are based off of windows, which seems likely for remote control
software, you could add a group policy to your PDC ( Primary Domain
Controller ) to restrict access to IE's properties and for a
configuration on the accounts you do not want to allow to tunnel, and
in that configuration specify to deny access to certain ip addresses
or url's.