There are several "historical" magic items which would make good artifact additions I think, but these can't be done based on what attributes can be modded or affected by items:
The Tarnhelm (A5 E4)
Adds glamour, stealth, and flight
maybe .secondshape Dragon to represent shapeshifting
The Palladium (N6 S3)
Large misc slot item (maybe 2 slots like the Arc)
Provides gigantic Supply and Fort Defence and Valor ++
Bag of Dragon's Teeth (F5 E2)
In combat, summons Heavy Infantry, or maybe Myrmidons
"Caladbolg" sword (E6)
Armor negating and area attack hits 3 squares
(one blow chopped off the tops of 3 hills)
We should have some more artifact ranged weapons, and some non-western legend items like Persian: Cup of Jamshid or Flying Throne of Kai Kavus. There's a
good list for looking over at wikipedia.
Sill