Actually, some of those are funny easter eggs... but anyway:
While in the simulator, press [Ctrl] + [Alt] + [Shift] + C. Then, a prompt box with a flashing cursor will appear in the top left corner of the screen. Type one of the following codes and press [Enter] to activate the corresponding cheat function:

sim = "If You Lived Here, You'd Be A Sim" message.
bat = "Da Da Da Da Da Da Da Da Da BAT-man!" message.
erts = "Investment Tip: Buy Low, Sell High" message.
sc3k = "Mayor Suspected Of Attempting Embezzlement; Ends In Failure" message.
1234 = "Secret Number Combination Causes Announcement In News Ticker" message.
fund = "FUND Not A Cheat Code, Do Not Type MOREMONEY, It Is Not A Cheat Code Either" message.
help = "Dozens Of Hidden News Ticker Reveals; Sims Encouraged To Collect Them All And Amaze Friends" message.
llama = "The Llama Is A Quadruped" message.
scurk = "If You Build It, They Will Come" message.
hello = "Greetings Mayor, Your Sims Salute You" message.
money = "Money Does NOT Grow On Trees, Study Concludes" message.
maxis = "Did you know that MAXIS spelled backwards is SIX AM?" message.
mayor = "Mayor (Name of Mayor) brings (Name of City) To News Ticker Highlight" message.
zyxwvu = SimCastle construction, if Vinnie's offer was declined.
ticker = "(Name of City) Picayune: The Finest In Scrolling Entertainment" message.
salt on = Change the sea to salt water.
simcity = "Keep Trying And Maybe You'll Figure It Out" message.
advisor = "Mayor Under Investigation For Possible Embezzlement" message.
salt off = Change the sea to fresh water.
broccoli = "Sorry, Money Doesn't Grow On Broccoli" message.
i am weak = Construction costs set to $0.
moremoney = "MOREMONEY Not Cheat Code, Research Concludes" message.
easter egg = "Duo Ragazzi's Easter Egg Palace: Old World Charm In A Post Modern Setting" message.
will wright = "What Will He Think Of Next?" message.
terrain one up = Raises the terrain by one.
terrain ten up = Raises the terrain by ten.
electronic arts = "Not Just Sports Games Anymore" message.
i love red tape = Description of City Hall set to "Miles and Miles of Red Tape"; date set to the year 1900.
terrain one down = Lowers the terrain by one.
terrain ten down = Lowers the terrain by ten.
porntipsguzzardo = "Aha! We Have A Real Pro Here! Try BROCCOLI" message.
let's make a deal = If you have connections to your neighbors, they will start trying to make deals.
call cousin vinnie = Donation offer from Vinnie.
stop forcing advice = Stops advice.
power to the masses = All power plants.
water in the desert = All water plants.
garbage in, garbage out = Recycling plant, waste to energy incinerator and normal incinerator.
pay tribute to your king = All extra gifts.
force gus to say (phrase) = Gus will say the indicated phrase.
force moe to say (phrase) = Moe will say the indicated phrase.
force karen to say (phrase) = Karen will say the indicated phrase.
force maria to say (phrase) = Marla will say the indicated phrase.
force randall to say (phrase) = Randall will say the indicated phrase.
force mortimer to say (phrase) = Mortimer will say the indicated phrase.
force constance to say (phrase) = Constance will say the indicated phrase.
force petitioners to say (phrase) = The petitioners will say the indicated phrase