The logging of TmG is good, but you can't see everything.
The only monitoringserver I use except build in windows is Cacti
Cisco has such advanced logging, but then you need to configure the vpn on the cisco router.
You can try Internet Access monitor
you need to install a bridge from your clients to the server
I am using it with TMG 2010 and Server 2008 R2.
IT issues often require a personalized solution. With Ask the Experts™, submit your questions to our certified professionals and receive unlimited, customized solutions that work for you.
Take hold of your future.