To use a cheat code, press the [Ctrl], [Shift], [Alt] and [C] keys at the same time. This will bring up a cheat window for you to type a code.

Turns out there is such a thing as a free lunch ...
CODE: i am weak
EFFECT: Makes buildings, utilities, zoning, transportation, planting trees and creating surface water free.

Something fishy about this guy ...
CODE: call cousin Vinnie
EFFECT: A new petitioner item will appear in the Meet window, announcing a "Local Fundraising Event." This, um, "businessman" will offer you some cash, no questions asked. Should you choose to accept his offer, you'll notice a little extra cash in your coffers -- but will you still respect yourself?

Instant Castle
CODE: zyxwvu
EFFECT: This code isn't available to just anybody, you have to prove your integrity first. Use the "call cousin Vinnie" cheat and refuse his immoral offer. Then use the "zyxwvu" cheat and the beautiful SimCity Castle will appear in your Rewards menu. In addition to looking cool, the castle boosts land value, aura, and does other wonderful things to the surrounding area.

Utility Time Machine
CODE: garbage in, garbage out
EFFECT: Makes all garbage buildings available, no matter what year.
CODE: power to the masses
EFFECT: Makes all power buildings available, no matter what year.
CODE: water in the desert
EFFECT: Makes all water buildings available, no matter what year.

Unlimited Flying Objects ...
CODE: UFO Swarm
EFFECT: After typing the cheat code, Set Disaster to UFO and watch an extreme number of flying saucers descend upon your city.

Bird's-eye View
CODE: The Birds
EFFECT: Look closely for a flock of seagulls flying above your fair city. And tell your Sims to cover their heads.

Industrial-strength Detergent ...
CODE: nerdz rool
EFFECT: Causes clean, high-tech industry to be built in your Industrial Zones.

All Buildings, All the Time
CODE: (You don't need the Cheat window for this one.)
Open and close the Power Plants menu
Open and close the Rewards & Opportunities menu
Open and close the Garbage Disposal menu
Open the Landmarks menu
EFFECT: When you open the Landmarks menu, you'll find that ALL the buildings in SimCity 3000 are now available to you!

Simon Says
EFFECT: The following codes cause the Newsticker to display something unusual.
CODE:
fund
advisor
moremoney
maxis
1234
sc3k
mayor
hello
simcity
money
ticker