Man I love the summons Carbuncle Ifrit Titan Leviathan Tetra Sylphid Ramuh Shiva Alexander Diabolos Siren Odin Fenrir Lakshmi Golem Anima Phoenix Asura Shinryu And of course my favorite Bahamut were just awesome
There's some I wish was in the game (also ones that would be good summons): Adamantoise Lich Maralith Kraken Tiamat Echidna Two-headed Dragon Ahriman Cerberus Mist Dragon Barbariccia (and the other elemental fiends who's names I can't remember) Syldra Gilgamesh Enkidu Atomos Omega Weapon Kirin Unicorn Maduin Bismark Valigarmanda Midgardsormr Typhon Zevan Sephirot Sophia Hades Kujata Knights of the Round Quetzalqoutal Pandemona Eden Madeen Ark Valefor Ixion Yojimbo Magus Sisters Garuda Brynhildr Hecatoncyris Ravana Genbu Seiryu Suzaku Byakko Salamander Cyclops And Zodiark