Turbo mode:
At the Autobot headquarters menu, press L1, R2, R2, , , , , L1.

Invincibility:
Pause then press R1, , , R1, R2, L1, L1, L2.

Unlimited stealth:
At the Autobot headquarters menu, press Up, Up, Down, Down, L1, L2, L1, L2.

Stealth enemies:
Pause then press Left, Right, Left, R1, R2, R1, Right, Right.

Unlimited powerlink:
At the Autobot headquarters menu, press Up, Down, Up, Down, , , , .

Disable mini-con overload:
At the Autobot headquarters menu, press R1, R1, L2, R1, R1, L2, , .

One hit kills:
Pause and press , , , , L1, L1, L2, L1.

All mini-cons:
At the Autobot headquarters menu, press L1, L2, , , , , L2, L1.

All extras:
Press , , , , , , L1, L2 at the extras menu.

Enter the following codes at the difficulty selection screen.

Alaska level completed:
Press R1, , R1, , Left, Left, Right, Left.

Amazon boss defeated:
Press Left, Left, Right, L1, R2, Left, Left, Right.

Amazon level completed:
Press L1, L1, L2, , , , R1, R2.

Earth level completed:
Press R2, R1, L1, L2, , , , .

Deep Amazon with six mini-cons:
Press Left, Left, Right, L1, L2, Left, Left, Right.

Deep Amazon with 13 mini-cons:
Press R1, R1, R2, L2, L1, L1, R1, R1.

Deep Amazon with 16 mini-cons:
Press , , , R1, L1, Left, Left, Right.

Deep Amazon level completed:
Press Left, Right, Left, Left, Right, R1, R2, .

Antarctica with 6 mini-cons:
Press L1, L1, L2, , , , R1, R2.

Antarctica Boss defeated:
Press L1, Left, L2, Right, , , , .

Antarctica level completed:
Press R1, R1, R2, L2, L1, L1, R1, R1.

Mid Atlantic with 17 mini-cons:
Press Left, Right, Left, Left, Right, R1, R2, .

Mid Atlantic with 18 mini-cons:
Press L2, Left, Right, Right, Left, L2, L1, L2.

Mid Atlantic boss defeated:
Press L2, Left, Right, Right, Left, L2, L2, L2.

Mid Atlantic level completed:
Press , , , , Right, Left, Left, Right.

Alaska with 18 mini-cons:
Press , , , , Right, Left, Left, Right.

Alaska with 23 mini-cons:
Press R1, R1, R2, L1, L2, L2, , .

Starship with 23 mini-cons:
Press R1, , R1, , Left, Left, Right, Left.

Starship with 24 mini-cons:
Press Right, Right, , R1, R2, , Left, Left.

Starship level completed:
Press Left, Left, Right, , , Right, Right, Left.

Pacific Island with 24 mini-cons:
Press Left, Left, Right, , , Right, Right, Left.

Pacific Island with all mini-cons:
Press L1, R1, L2, R2, Left, Right, .

Cybertron with all mini-cons:
Press R2, R1, L1, L2, , , , .

Thanks to Revolution readers Jacob Schwalbe, and Van Desiel!