To Date, there have been 21 FF Games released:
FF 1 -12
FF 10-2
FF Tactics
FF Tactics Advance
FF Crystal Chronicles
FF Mystic Quest
FF 7 Before Crisis
FF 7 Dirge of Cerberus
FF 7 Dirge of Cerberus Lost Episode
Seiken Densetsu: Final Fantasy Gaiden (later became its own series, but was originally intended as an FF spinoff)
(20) There are a further 7 expected soon:
FF 13
FF 7 Crisis Core
FF 12 Revenant Wings
FF 13 Agito
FF Versus 13
FF Crystal Chronicles: Ring of Fates
FF Crystal Chronicles: The Crystal Bearers
(27) There are a further 6 titles released under the FF name
3 expansions for FFXI
3 SaGa games released under the FF brand in the west
(33) There have been 18 releases of remakes
6 of Final Fantasy
4 of FF 2
1 of 3
3 of FF 4
2 of FF 5
2 of FF 6
(51) There have been 5 properties in the film/tv medium.
FF The Spirits Within
FF7 Advent Children
FF7 Last Order
FF Unlimited
FF Legend of the Crystals
(56) There have been 14 non-FF branded games that feature FF characters or locations:
9 Chocobo Games
Ehrgeiz
Vagrant Story (Valendia is in Ivalice)
3 Kingdom Hearts games
(70) There were 4 "International" editions of the above
FF7
FF10
FF10-2
KH: Final Mix
(74) There were 4 platform ports of certain titles
FF7 (PC)
FF8 (PC)
FF11 (PC, Xbox)
That makes 78 Final Fantasy releases at most.
edit: forgot the international editions and PC/Xbox ports.