It's often argued by gun lovers that it's the Second Amendment that keeps us free, despite their inability to point to any actual historical evidence that there is any link between private gun ownership and political freedoms.
Over at PoliBlog there's a good discussion brewing. http://www.poliblogger.com/?p=16089
In fact there is such a disproportion between the military tools available to the modern state and what citizens could have that there's zero chance of successful armed resistance in the face of unified authorities. The examples of Waco and the Philadelphia MOVE siege provide stark reminders that even well-armed and reasonably large grouping of private citizens can't prevail in direct combat against police forces -- let alone actual military units. This was even true in the eighteenth and nineteenth century. Washington quickly suppressed the Whiskey Rebellion, which involved a very substantial number of people for the time and militia forces were very instrumental in suppressing labor movements in the 1800s. It only took a few regiments of combat veterans to restore order in New York during the 1863 draft riots.
Really, gun supporters need to identify some historical cases where private gun ownership made a differences.
That said, I do think there's a good case to be made for private gun ownership for personal protection against violent crime, particularly in cases where physical remoteness from help or ineffectiveness or corruption of local police make it necessary.