The first method, I feel, is the least intrusive and most useful: assuming iTunes is running, all you need to do is hold down cmd+opt (possibly ctrl+alt on Windows, though I don't have a machine to test that on) when connecting your iPod to make iTunes look the other way and not begin a sync. The iPod should mount on your desktop and even appear in iTunes, but it simply won't sync. You're free to go about your business and eject the iPod as quickly as it mounted, with no argument from iTunes.
The second method assumes that you have enabled hard drive use for your iPod, and you don't have iTunes set to automatically start when you plug the 'pod in. In this case, simply quitting iTunes when plugging in your iPod will solve your problem altogether. Simply do your business and eject to get on your way quickly.