The following cheats will work with all known versions of SimCity 4. To activate these cheats, press CTRL+X to bring up the cheat input box, then enter the desired code and press enter.

DollyLlama - Gives city planners llama heads
fightthepower - Operate your city without any electricity requirements.
GOL - green plasma effect
hellomynameis <name> - Reset the name of the mayor to the given value.
howdryiam - Operate your city without any water requirements.
recorder - Start the recorder
sizeof <zoom> - Change the game magnification to the given value. Acceptable values are 1-100.
stopwatch - Pauses the 24 hour clock cycle. Enter it again to resume the timer.
tastyzots - Toggles zots (cell warnings)
weaknesspays - Gives you §1000 simoleons
whatimeizit <hour> - Set the 24 hour clock to a specific time of day.
whererufrom <name> - Reset the name of your city to the given value.
you don't deserve it - Make all rewards available, even if you truly don't deserve them.
zoneria - Hides the coloring of undeveloped zoned tiles.

(Yes, I finally got SC4 to install on my desktop system!)