There is a place in Cocoon called Eden, which was a GF from FFVIII. Also from FFVIII is the Lionheart gunblade that Lightning can equip.

The ultimate weapon that Vanille can get is the Nirvana which was Yuna's ultimate weapon from FFX.

Lionheart's upgrade is the Ultima Weapon, which I know what a weapon that Zidane had as his strong weapon I think. Not to mention the fact that Ultima and Omega Weapon have been used as end game bosses in several FF games in some form of the name.

Vanille has Full Cure which was an ability that Selphie had if I remember right.

Fang's ultimate weapon is called Kain's Lance, which I think is referring to FFIV's Dragoon character Kain.

Snow's ultimate weapon is Save the Queen which is the name of a sword that Steiner can use in FFIX.

One of Hope's weapon is called the Simurgh which is a HNM from FFXI and one of Lightning's weapons is the Durandal which is the best purchasable weapon that a Paladin can use in FFXI.