A-12 Avenger 2
The A-12 Avenger 2 is a futuristic plane capable of blazing speed. On the Xbox 360, you can unlock it by going to your Hanger in the game, holding down LT, and then sequentially pressing X, LB, X, RB, Y, X. To unlock it on the PlayStation 3, go to the Hanger, hold down L2 and then press Square, L1, Square, R1, Triangle, Square. On the PC, go to the Hanger, hold down the "Shift" key, and then type "xaxdqx".
F-18 HARV
The F-18 HARV is an experimental aircraft that you can unlock only with a secret code. On the Xbox 360, go to the Hanger, hold down LT, and then press LB, Y, LB, Y, LB, X. On the PlayStation 3, hold down L2 and then press L1, Triangle, L1, Triangle, L1, Square. To unlock the plane on the PC, hold the "Shift" key down and then type "aqaqax".
FB-22 Stike Raptor
The FB-22 Strike Raptor is the fastest, strongest, most powerful plane in the game, and you can unlock it only by entering a secret code at the Hanger. On the Xbox 360, hold down LT and then press RB, X, RB, X, RB, Y. On the PlayStation 2, hold down L2 and then press R1, Square, R1, Square, R1, Triangle. On the PC, hold down the "Shift" key and type in "dxdxdq".
Other Unlockables
You can unlock other planes by achieving certain levels in the game, which you earn based on how many missions you complete. Reaching all the way to level 40 will unlock 49 different planes, including the SU-37 Terminator, F-22 Raptor and several MIRAGE class aircraft. By reaching level 13, you will unlock 17 different weapons packs, which you can use to upgrade your planes.