While collecting your Protectorate of Menoth army, you will see use out of certain models again and again. Starting with the Protectorate of Menoth Battlebox, the following models are also solid additions to any Warmachine army.
What to Order
Warjack Support
Choir of Menoth

- PIP 32005 (Leader and Acolyte) PLUS
- PIP 32006 (purchase 1 acolyte blister for a minimum unit, 2 for a full unit)
- PIP 32087 (Full Unit, Leader and 5 Acolytes)
There are few mandatory units in the Menite army, but you'd be hard-pressed to find a Protectorate list without this unit. Their hymns are fantastic for the Menite 'jacks, and can easily negate the strengths of your opponents, as well as buff your 'jacks with The Battle Hymn. One key thing to remember is that the Choir can target multiple warjacks, but they have to use the same hymn.
Vassal of Menoth

The Vassal protects your warjacks with Enliven and increases their offensive potential out of activation by giving a warjack an Ancillary Attack.
Tarpit Unit
Temple Flameguard

- PIP 32018 (6 models)
- PIP 32010 (2 blisters of 2 models each)
Temple flameguard can receive the Shield Wall Order to become a solid ARM 17 with the Set Defense Ability. Temple Flameguard can hold off most infantry advances and can even put hits onto heavy warjacks with charges and the combined melee attack ability.
Combat Unit
Knights Exemplar

The Knights Exemplar are Menoth's blade on Caen, and it shows in their melee capabilities. P+S 11 Weapon Masters is hardly anything to scoff at, and both infantry and warjacks alike will feel the pain. However, their main ability is the buff they receive when members of the unit dies. If properly deployed and positioned, Knights Exemplar can prove to be a massive headache that becomes more threatening as your opponent attacks them.
Ranged Warjack
Redeemer
Warcaster Support
Hierophant

Hierophants help you manage focus by reducing the cost of a cast spell by one. In a pinch the Hierophant will heal your warcaster to keep them in the fight.
Conclusion
Familiarize yourself with these Menite tools, and you'll find a place for at least some of these models in many of your Menite armies.