I don't know what the rules in Races of Stone look like, but we could always devise our own feats and iconic armours.
Skin of Yzakaush
After slaying the seemingly impervious demon Yzakaush, the unnamed warrior fashioned the demons rigid hide into a suit of full plate that he donned before heading off to fight in the war plaguing his country. The demon's skin provided exceptionally good protection, but when the warrior had donned it, it fused itself to him, and he was unable to remove it. Furthermore, every night he was plagued by nightmares. Eventually, madness took over and he was slain while attacking a legion of warriors single-handedly.
The Skin of Yzakaush is a cursed suit of full plate armour. It functions as +5 full plate of fortification and invulnerability. Because it fuses itself to its wearer, it allows slightly better movement, having a max Dex bonus of +2 and an armour check penalty of -4. It is treated as medium armour for the purpose of sleeping in it, so someone possessing the Endurance feat would have no problem in this respect. Every night though, the wearer is affected by an effect identical to the nightmare spell, with the maximum -15 penalty (effective Will DC = 32). However, if the wearer manages to make the save for seven nights in a row (becoming immune to the spell does not count as a save), they will no longer be affected by nightmares.