And a little variation on a suggestion I saw a long time ago:

When you're out exploring kind of early and spot that attractive distant landmass that's closer to the ai than you, hustle back with a settler, a diplomat, a defender, and a mobil unit. Build a fortress on good terrain for the units and diplomat and road one square. Head for one of the good city locations, build the city and wait for the barbarians. They'll show soon enough and take the city. And you'll have a steady supply of "Non" units until you can return with more settlers to prepare other city sites - the barbs'll keep the ai out 'til you're ready. Then incite revolt in the barb city, found the others on prepared sites, get some love, and you've got some nice distant cities well defended with non units.

As I got close Barbarians captured Moscow. At first I thought I'd bribe it, getting a cheap city in enemy territory. But when I got near I realized what a goldmine it could be. I sent my settler back because I didn't want to have the closest city. I put my defender on a mountain between the Barb city and the other Russian cities, so the Russians couldn't take it back. I placed my diplomat a few squares away from the Barb city and started bribing units -- getting a regular supply of NONs.

I've used it the whole game -- must have gotten 30 NON units. I got Leo's, so they kept getting upgraded. The only drawback is that, except for two elephants, they were all defensive units. Still, all my cities and choke points are defended by NON units, and the only supported units are my attackers.