Esper Locations
    I have tried to put these in the order in which you get them but in the World of Ruin there is no set order in which you need to go.  All of the Espers in the first section are in the order that you should get them.
Ramuh - Zozo Tower
Kirin - Zozo Tower
Siren - Zozo Tower
Stray - Zozo Tower
Ifrit - After Defeating Shiva and Ifrit in the Magitech Factory
Shiva - After Defeating Shiva and Ifrit in the Magitech Factory
Unicorn - Magitech Factory
Bismark - Magitech Factory
Shoat - Magitech Factory
Carbunkl - Magitech Factory
Phantom - Magitech Factory

Sraphim - Buy in upper part of Tzen
Starlet - Bookshelf in Ozer's House
Phoenix - End of the Phoenix Cave
Palidor - Solitary Island Beach after you find the airship
Maduin - Zozo Tower (post Terra's memory)
Odin - Ancient Castle
Raiden - Ancient Castle (5 steps down from the throne, down the stairs)
Crusader - After defeating all 8 dragons
Bahamut - After defeating Doom Gaze
Alexander - Doma Castle behind the throne after Cyan's dream
Ragnarok - Weapon shop, Narshe
Terrato - Umaro's bone carving
Zoneseek - Auction House, Jidoor (world of ruin)
Golem - Auction House, Jidoor (world of ruin)
Fenrir - After battling Phunbaba in Mobiz