Lesser Summons:(remain on the field three turns)
Worg:
A small wind aligned wolf capable of flight. They are able to cast basic body and wind magics.
Dragon Sprite: 
Just as their name suggests, these summons are tiny elemental dragons. Because of their young age however, their attacks are mediocre at best.
Hippogryph:
These eagle/horse hybrids are known for their sharp temper and their even sharper talons. While powerful in their own right, they are only capable of physical attacks as magic is beyond their grasp.
Cockatrice:
These birds summons are capable of performing some rather potent status magic. Their most famous attack turns the enemy into stone.
Unicorn:
These gentle beasts will not fight actively but are able to perform potent healing magic.
Greater Summons:(remain on the field two turns)
Hell Cat: 
These vicious felines are capable of potent fire attacks and are best know for their burning fur which sets enemies alight when they touch it.
Gryphon:
The cousin of the hippogryph, these eagle/lion hybrids are easily capable of ripping a human to shreds with their impressive talons. Being a good deal more powerful than their cousins, they are able to perform boost magic enabling them to strengthen themselves.
Rainbow Caller:
These strange bird-like creatures are capable of causing damage from any element. They are however, "paper tigers" and cannot stand up to physical damage.
Kitsune:
Little more than magical foxes, these beasts pack a rather surprising wallop. The more powerful the kitsune, the more tails it will possess with nine being the max amount. Being able to cast many different magics because of this makes them a favorite as a back up caster.
High Summons:(remain on the field one turn)
Genbu:
The Lord of Earth elementals, his attacks are capable of devastating a landscape in one strike.
Byakko:
The Lord of Lightning elementals, his control over his element is unrivaled by any other summon.
Seiryuu:
The Lord of Water elementals, He is the only high summon capable of healing magics alongside his powerful elemental attacks.
Suzaku:
The Lord of Fire elementals and the hardest normal summon to control. His immense hatred of mortals makes him a risky choice at best. Once you gain his loyalty however, he is easily the most powerful of the four high summons. Summoning him will always knock the summoner out afterward because Suzaku takes a small chunk of life energy from his summoner upon being dismissed as a "tax".
Special Summons:(These require more than one summoner to call and only remain for one turn)
Tiamat:
This engine of pure draconic destruction requires 3 summoners to call on her. Capable of performing 5 attacks in one turn, she is the ultimate elemental summon.
Dragon Paladin:
A dragon that has encased his entire body in holy armor. Not only able to attack using holy magic, this powerful creature is able to perform high leveled healing magics. He requires two summoners to bring him into the mortal realm.
Chaos Dragon:
This dragon represents Chaos incarnate. The polar opposite of his holy counterpart, this dragon specializes in powerful dark magics. He is also able to cast powerful status and illusions magics. This summon is never in the control of its summoners and is just as likely to turn his attacks on him as he is to destroy the enemy. If his help is needed, two summoners are needed to call him from the darkest reaches of the summoning plane.
Bahamut:
The Lord of Dragons and the only time magic wielding summon. This massive dragon can only be called by 5 summoners working together. Bahamut, like his powerful child, the Chaos Dragon, is not controlled by his summoner's whim. Unlike his child, he is more ambivalent towards summoners and is less likely to turn his powerful magics onto his summoners. His powerful time magics are backed up by his immense strength and size. He is truly a summon that few have lived to tell about.