1, crystal chronicles for the ncg. (not that rare, but expensive bought IRL. outsource online.)
2, crystal bearers and echoes of time for wii. (nowhere near as bad as ngc game costs, but as it's a franchise, watch out for IRL gougers. again, outsource.)
3, dirge of cerberus for the ps2. (surprisingly cheap for part of the ff7 story, and in absolute fairness despite the change of gameplay, definitely worth having.)
4, crisis core for the psp. (i've never ever seen a retail copy of this game in the shops near me, ever. like gradius 3 & 4 on the ps2, it's VERY elusive. outsource.)
5, ............. dissidia for the psp. (not so much an rpg, but a beat em up, good as an intermission, and features many characters of the ff franchise.)

[edit]
typo.