This code will enable you to have access to all the buildings.While playing, press Left C, then hold A + Right C. If entered correctly, you will hear a voice give you the new building options.
Be able To Build Opponent's Units
Get your engineer to take over a enemies construction yard and you can build their units.
Buy the Tiberium Factories
When you destroy all your opponents Tiberium Factories, you can shoot one of their structures a few times and they will sell it to you. However, make sure that you take out their main base first or they will not be able to rebuild the Tiberium factories.
Easy Money
The Churches in the villages have 1000$ in them. Destroy them to get the money.
Economics 101
It is $100 dollars cheaper to build two regular power plants than one advanced power plant you get just as much power with thicker armor.
Faster Ion Cannon and Nuclear weapons charge
Build many power plants and the more you have the faster the weapons will charge.
Level Select
At the title screen where players see "press start" enter the following code using the control pad: b, a, r, r, a, c-right, up, down, a. There will be no indication that the code worked. Press start and go to replay mission. Press L and then choose your side and mission.
More Money: Silo
Just build an engineer and take over your enemies silo to get the money that is stored in their silo(s).
Sandbagging trick
Use sandbags to build all the way to your enemies base. Now build some defenses, guns or whatever to take them out! A ton of turrents is especcially effective!
Zoom It
Hold L press C-Up or C-Down to zooom in and out of the battlefield.