The Espers Belias, the Gigas-Location: Tomb of Raithwall (story)
Mateus, the Corrupt-Location: The Stilshrine of Miriam (story)
Shemhazai, the Whisperer-Location: Giruvegan (story)
Hashmal, Bringer of Order-Location: The Pharoes-third ascent (story)
Famfrit, the Darkening Cloud-Location: The Pharoes-third ascent (story)
Adrammelech, the Wroth-Location: Zertinan Caverns (side quest, "Paying for the past")
Cuchulainn, the Impure-Location: Garamsythe Waterway (side quest, "Lost in the Pudding" hunt and "Sluiceway Search")
Chaos, Walker of the Wheel-Location: Necrohol of Nabudis (side quest, "Waterway Haunting," Lost in the Pudding" and "Broken Artifact")
Zalera, the Death Seraph-Location: Terminus no. 7/Barheim Passage (side quest, "Dalmasca's Desert Bloom," "Pursuit of a Cure" and "missing Ferryman")
Zeromus, the Condemner-Location: Mt Bur-Omisace (side quest; collect the Stone of the Condemner)
Exodus, the Judge-Sal-Location: Mosphoran Highwaste (side quest; solve floatweed puzzle in Mosphoran Highwaste)
Ultima, the High Seraph-Location: Giruvegan (side quest; hidden in Giruvegan's Great Crystal)
Zodiark, Keeper of Precepts-Location: Henne Mines (side quest; must acquire at least 10 other Espers)
Thank You,
If you have any questions on any of these just ask and ill get back to you.