Here are the summons that are featured in FFXII:

BELIAS

Devil Berias
Element: Fire
Zodiac: Aries
Level 1
Technique: Pain Flare,
Deathblow: Hellfire. {time-death}

CHAOS

King of Reincarnation
Element: Wind
Zodiac: Taurus
Level 3
Technique: Tornado,
Deathblow: Hurricane. {time-death}

ZALHERA

Angel of Death
Element: Death
Zodiac: Gemini
Level 1
Technique: Kill,
Deathblow: Divine Death. {1/4 remaining HP}

ZEROMUS

Convicted Tyrant
Element: Gravity
Zodiac: Cancer
Level 2
Technique: Black Perishing Circle,
Deathblow: Big Bang. {time-death}

HASHMALIM

Regulator
Element: Earth
Zodiac: Leo
Level 2
Technique: Rock You,
Deathblow: Terrestrial Rage. {Caster must be near death, red HP}

ULTIMA

Holy Angel
Element: Holy
Zodiac: Virgo
Level 3
Technique: Destruction,
Deathblow: Perfect Ultima. {Both Caster and Summon must be near death, red HP}

EX-DEATH

Sacred Tree Of Judgement
Element: Non-Elemental
Zodiac: Libra
Level 2
Technique: Comet,
Deathblow: Meteo. {Cast on Summom: Don't Move}

CUCHRAIN

Tainted King
Element: Poison
Zodiac: Scorpio
Level 2
Technique: Insect Poison Miasma,
Deathblow: Venom Bite. {time-death}

SHUMIHAZA

Betrayer
Element: Soul
Zodiac: Sagittarius
Level 2
Technique: Loading Attack,
Deathblow: Soul Emit. {time-death}

ADRAMMELECH

Raging Sacred Emperor
Element: Thunder
Zodiac: Capricorn
Level 1
Technique: Flash Cannon,
Deathblow: Judgement Bolt. {time-death}

FAMFRIT

Dark Cloud
Element: Water
Zodiac: Aquarius
Level 3
Technique: Pale Bombardment,
Deathblow: Tidal Wave. {time-death}

MATEUS

Corrupt Emperor
Element: Ice
Zodiac: Pisces
Level 1
Technique: Frozen Heavenly Attack,
Deathblow: Freezing Wave. {time-death}

ZODIAC

King Of Commandment
Element: Dark
Zodiac: Serpentarius
Level 3
Technique: Vanish Ray,
Deathblow: Last Eclipse. {Summoner must be in Petrifying Condition}

Credit: Gamespot