Sets of Unique Armor

Valyrian Steel Armor is worn by Euron Greyjoy of the Iron Islands. It can be obtained by killing him or sending him to the wall if you own King's Landing

Kings Guard

Kings Guard armor is accessible if you own King's Landing. You can buy it through the faction blacksmith in the town.

Gold Cloak

Gold Cloak armor is accessible if you own King's Landing. You can but it through the faction blacksmith in the town. (they wear the same mittens and boots as the Kingsguard)

The Mountain

The Mountain (Ser Gregor Clegane) wears one of the best pieces of armor in the game. You can obtain it by sending him to the wall or executing him.

Mace Tyrell

You can obtain it by sending him to the wall or executing him.

Brog Matter

You can obtain it by executing him after doing "Bringing a Warlord to Justice".

Princess Khiarai

Acquired from Princess Khiarai. When Princess Khiarai is recruited as a companion it can be taken off of her.

Individual Armor Pieces

Helmets

Crown of the Seven Kingdoms

You can obtain it by sending King Joffrey Baratheon to the wall or executing him.

Aegon Targaryen Helmet

You can obtain it by sending him to the wall or executing him.

Body Armor

Brienne's Plate Armor

Acquired from Brienne of Tarth. When Brienne is recruited as a companion it can be taken off of her. The armor is a heavy plate armor that has a golden chestplate and pauldrons, steel arm guards, golden elbow plates, and a blue bottom kilt-esque feature that compliments the top. This armor is one of the best plate armors in the game stat wise.

Targaryen Plate Armor

Chest 52 - Legs 24 - Acquired by killing the Hedge Knights in Varys's questline, he will give it to you as a reward. The armor is a heavy plate chestplate that is dark grey in color. Upon the chest is the sigil of House Targaryen, the 3 headed dragon. The armor looks very simplistic but effective overall, with only the body area and shoulders having any real protection, the arms covered by leather. The armor will look different depending on if you choose the book or show version. The book version is red whilst the show is grey. Looking similar to the Kingsguard armor worn by Ser Arthur Dayne in the GoT tv series