Forza 4 Official Unofficial Car list.
Well here is a currently known car list for Forza 4, since no-where elso in the interweb seems to have one, i'll do mine from memory and videos, so, if anyone sees any others and can prove it (or for car model versions etc.), let me know, other mods, admins can feel free to change it!
Alfa Romeo
2011 Alfa Romeo Giulietta Quadrifoglio Verde (Numerous outlets (Pre-order))
Aston Martin
Aston Martin One-77 (Top Scores, E3) Class - S686
Audi
Audi R8 5.2 (Top Scores, E3) Class - S666
BMW
(**Forza 4 Has an exclusive BMW deal, there will be a special edition pack including 25 extra cars)
2012 BMW M5 (Forza 4 exclusive BMW pack)
BMW 1-Series M-Coupe (Forza 4 exclusive BMW pack)
Bugatti
Bugatti Veyron (Video, E3)
Cadillac
Cadillac CTS-V (Opponent, E3)
Chevrolet
Chevrolet Camaro (Opponent, E3)
Corvette C6 Z06 (Top Scores, E3)
Class - S662
Citroen
Citroen C4 (E32010, track day)
Dodge
Dodge Viper (Opponent, E3)
2010 Dodge Challenger (Top gear)
Ferrari
2002 Ferrari Enzo (AutoVista, E3)
Ferrari 458 italia (Cover Car)
Ferrari FXX (Spoken, E3)
Ferrari California (Video, E3)
2011 Ferrari 599 GTO (Spoken, E3)
Class - S692
Ferrari F333 SP (File Import Poster car)
Fiat
2010 Fiat 500 abarth esseesse (Award car, E3)
Ford
Ford Focus (E32010, track day)
2005 Ford GT (Video, trailer)
Ford Mustang GT (Opponent, E3)
2009 Ford Fiesta Zetec S (Award car, E3)
Gumpert
Gumpert Apollo (Video, E3)
Honda
Honda Civic (Track Day, E3)
Honda Fit (Track Day, E3)
Jaguar
Jaguar XF (Hot Lap Poster Car)
Jaguar CFR (X360 magazine preview)
KIA
KIA Cee'd (IGN report, E3)
Koenigsegg
Koenigsegg CCX (Video, E3)
Lamborghini
Lamborghini Reventon (Video, E3)
Lamborghini Murcielago SV (Video, E3)
Lexus
Lexus LF-A (Video, E3) Class - S649
Lotus
Lotus Evora (Opponent, E3)
Mclaren
1993 Mclaren F1 (Picture, E3)
Mclaren MP4-12c (Video, E3)
Mercedes
Mercedes A-Class (E32010, track day)
Mercedes SLS AMG (Video, E3)
Class - S649
Mercedes SLR (Video, E3)
Mercury
1970 Mercury Couger (Spoken, E3)
Class - E273
Mitsubishi
2010 Mitsubishi Colt Ralliart (Award car, E3)
Mitsubishi Evo 10 (Opponent, E3)
Morgan
Morgan Aero Supersports (Rivals Alerts Poster Car)
Mosler
Mosler MT900s (Picture, E3)
Nissan
Nissan 370Z (Opponent, E3)
Nissan GT-R (Video, E3)
Class - S583
Nissan Versa (Track Day, E3)
Pagani
Pagani Zonda (Launch Trailer)
Spyker
Spyker C8 Laviolette (Video, trailer)
Subaru
2011 Subaru Impreza WRX STI (Driven, E3)
Class - B488
Toyota
Toyota GT (Picture, E3)
TVR
TVR Sagaris (Picture, E3)
As i say, memory only, i'll be contnuing to add throughout the year, and hopefully people can help too!