The following codes work for both GDI and NOD disks...

All FMV:

Enter the password cinema. Then go back to the password screen and enter whoami, sg, or jc to give access to comments and all full motion video.

To access Covert missions:
Enter the password covertops. The fun never ends...

Freaky Mission:
Enter the password patsux. Whoa, freaky mission indeed.

Instant Ion Cannons:
Right, Down, Left, Left, Down, Right, Right, Down, Left, X, Square, Triangle

Instant Air Strike:
Right, Down, Left, Left, Down, Right, Right, Down, Left, X, Square, Circle

Instant Nuclear Strike:
Pause the game and press:
Right, Down, Left, Left, Down, Right, Right, Down, Left, X, Up, X

For an Extra $5000:
Right, Down, Down, Left, L1, Left, Right, Down, Left

I think I'm turning Japanese:
Enter the password godzilla for some language changes...

Full Map:
Pause the game and press:
O, O, O, Up, O, Square, R1, O, O, O