I'm often building lab environments that have no ability to get online. This is usually because some of the VMs I build have the same name as actual production systems. Some of them are even restores of production VMs in a lab environment. Naming conflicts suck, especially in the middle of the day.
I found a great tool called WSUS Offline Update that lets me put all of the WSUS updates I want onto a virtual DVD and update my OS from it. I wish I had it back in the day when I was updating remote offices on a slow and shared internet connection! It's well-built and fairly granular - you can pick and choose OS, Architecture, etc. It will even do Office and .NET!