Instant building:
Hold [Ctrl] and attempt to build over objects.
Information in this section was contributed by lucas.

Keeping citizens happy:
To keep the citizens happy with you as mayor, lower taxes to zero. Just before the end of the fiscal year (December 31), pause game play and raise taxes to the maximum. . Then lower them again in January. Taxes are not collected until the end of the year, so they do not have to be raised to the maximum until that time.

$10,000:
Hold [Shif and type fund. Note: Enabling this code more than eight times in a row will result in an earthquake. To avoid this, enter the code up to eight times while the game is paused to collect $80,000. Then, save the game, exit, reload the game, and repeat the code as needed. Note: It does not matter how many times the code is entered, the maximum amount that can be collected is $80,000. The game must be paused, saved, and reloaded each time the code is entered.