You don't need nearly as much AC as you might think. Most armies will not have significant numbers of fighters or warriors above fourth level. And a typical 4th level fighter or warrior will have no more than a +8 attack bonus (14 str, weapon focus, masterwork weapon) and will probably deal 1d8+2 points of damage (average=7.5) with his one-handed weapon. So, some combination of AC 27 or 28 and/or DR is what you would look for.
So, between a ring of protection +5 a +5 amulet of natural armor and +8 bracers of armor, the Conan wannabe will have his requisite AC. (And the typical Frank Frazetta or Boris Vallejo barbarian is wearing metal bracers, a prominent necklace--the sometimes present gloves could be gloves of dexterity to make up for the ring if you're not willing to add one). To do even better, some of the barbarians in the pictures wear shields. A shield of Invulnerability would add some DR to the picture.
To round out the equipment, add a monstrously large and gaudy +6 belt of giant strength and a +5 adamantium weapon and fur boots (boots of the winterlands).
Add Great Cleave (or supreme cleave if you're willing to go for prestige classes) and you're ready to go. The elite members of the army can only hit him on a natural 20, when they do hit, they need to do average damage in order to inflict any damage at all, and the conan wannabe can kill eight to thirteen of them per round (great cleave 8 on the first attack and then five foot step before the second attack and cleave 5 or so more).
