Posting all of this 'cause I find it interesting. (And thus easy to go to having all links in one post!)
http://wiki.ffxiclopedia.org/wiki/Category:Avatars
Garuda:
http://wiki.ffxiclopedia.org/wiki/Garuda,_The_Queen_of_Birds-A_Tale_of_Granted_Wishes
Shiva:
http://wiki.ffxiclopedia.org/wiki/The_Ice_Queen_Shiva-A_Tragedy_of_Treason
Levithan:
http://wiki.ffxiclopedia.org/wiki/Leviathan,_Guardian_God_of_the_Sea
Titan:
http://wiki.ffxiclopedia.org/wiki/The_Legendary_Giant_Titan
Ramuh:
http://wiki.ffxiclopedia.org/wiki/The_Hermit_Ramuh
Ifrit:
http://wiki.ffxiclopedia.org/wiki/The_Transformation_of_Ifrit
http://wiki.ffxiclopedia.org/wiki/Category:Avatars
Garuda:
http://wiki.ffxiclopedia.org/wiki/Garuda,_The_Queen_of_Birds-A_Tale_of_Granted_Wishes
Shiva:
http://wiki.ffxiclopedia.org/wiki/The_Ice_Queen_Shiva-A_Tragedy_of_Treason
Levithan:
http://wiki.ffxiclopedia.org/wiki/Leviathan,_Guardian_God_of_the_Sea
Titan:
http://wiki.ffxiclopedia.org/wiki/The_Legendary_Giant_Titan
Ramuh:
http://wiki.ffxiclopedia.org/wiki/The_Hermit_Ramuh
Ifrit:
http://wiki.ffxiclopedia.org/wiki/The_Transformation_of_Ifrit