Ifrit: Summon forth The Lord of the inferno - Deals massive single target Dps with Hellfire.

Titan: Summon forth The Lord of the Crag - Creates an impenetrable Rock Skin around the tank giving invulnerability for unspecified amount of time, whilst dealing small aoe damage when he was summoned via his Earthquake when he lands or erupts on the battlefield.

Leviathan: Summon forth The Lord of the Whorl - using the tumultuous waves of the ocean, Leviathan creates a Tsunami which deals massive AOE damage and causes an unspecified Debuff to all those caught in it's path.

I could go on and suggest plenty of Summons and what there specific utility/damage could be to fulfill different roles and situations as the potential is Huge!.