Well, there's quite a few in here already, some are blatantly obvious, others are more subtile.
For instance, there's the whole Final Fantasy III's crystal tower now with all the monsters and bosses from there too.
The Gold Saucer is a direct reference to Final Fantasy VII's Gold Saucer, however it more than likely differs in appearance and options greatly. We'll have to see.
Magitek technology from Final Fantasy VI is everywhere to be found as well. Not being in any other game since.
Costa Del Sol is more than likely a direct reference to VII's Costa Del Sol (even though this one is an outpost with some scaffolding, and that one was a big town).
Limitbreaks, big Buster Swords being swung, Final Heaven, Meteor, etc.
Cid, Wedge and Biggs because, it's a final fantasy game.
All the references to Final Fantasy XI despite them upholding that it has nothing to do with XIV. (minions, cross-over events, races, jobs, abilities, similar stuff)
____________________________
[XI] Surivere of Valefor
[XIV] Sir Surian Bedivere of Behemoth
http://na.finalfantasyxiv.com/lodestone/character/2401553/