This is the final composite of Final Fantasy VII characters represented by Futurama characters similar to a common poster/wallpaper/image of the nine playable characters, as drawn by Nomura Tetsuya.
From left to right, the characters are:

1. Cait Sith = Nibbler riding Robot 1-X
2. Aerith Gainsborough = Fry's Ex-Girlfriend Michelle
3. Vincent Valentine = Bender Bending Rodriguez
4. Yuffie Kisaragi = Amy Wong
5. Nanaki (aka Red XIII) = Dr. John Zoidberg
6. Cloud Strife = Philip J. Fry
7. Cid Highwind = Zapp Brannigan
8. Tifa Lockheart = Turanga Leela (Elsewhere portrayed as Amy WongHere by The OnlyBezo
9. Barrett Wallace = Hermes Conrad

Of course, in this imaginary crossover universe, every character, not only the main nine, has a counterpart, for example,
President Shinra would be President McNeal
Rufus Shinra would have to be Nixon carried by the headless body of Agnew
Marlene = Dwight (even though Marlene and Barrett aren't related by blood and Dwight's not a girl...)
Lucrecia = Lucy Lui (because she's the only woman seen with Bender in more than one episode)
JENOVA = MOM
Sephiroth = Professor Farnsworth
Reno & Rude = URL & Smitty
Professor Hojo = Professor Wernstrom
Seto = Harold Zoid
Shera = Kif
Highwind = Planet Express Ship
Meteor = Big Ball of Garbage ("El Stinko")
Dyne = Barbados Slim
Kadaj = Walt OR Nudar
Yazoo = Larry OR Fleb (The taller scammer nudist)
Loz = Ignar OR Shlump (The shorter scammer nudist)
Zack = Yancy Fry
Zangan = Master Fnog
Don Corneo = HedonismBot
Heidegger = Morbo
Scarlet = Linda
Choco/Mog = A Lovey Bear riding a Buggalo, meaning all chocobos are buggalo and all moogles/mogs are Lovey Bears (certainly cute enough)
Titan = One of the largest Amazonian women
Bahamut = Pazuzu
Knights Of The Round = The Harlem Globe Trotters, with Bubble Gum Tate as Arthur


As far as limit breaks, Tifa/Leela's are about the same anyway. One of Bender/Vincent's could be to morph into a werecar, which would be awesome, or into Coillette: Grand Duchy of Robonia, which would be awesome in its own way.

Other key characters are hard to place; comments on who should be who are welcome. Everybody from Joe the Chocobo guy and Father Changstein El-Jamal to Tinny Tim and Genesis.

Also, in a highly related matter, LaTopazora has turned The Simpsons into the same characters, here and here, with a great Sephiroth choice.