SimCity

$10,000:
Hold [Shift] and type fund during game play Note: Enabling this code more than nine times in a row will result in an earthquake. Note: Some versions require the code to be enabled at the title screen.

Extra tax money:
Set the citizen's taxes to 0% just before tax collection (December or November if playing at fast speed). Set the taxes up to 20% just before they are due, then set the taxes back to 0% after collection.

Build on water:
Locate a straight horizontal or vertical stretch of coastline. Set up a powerline along the land. Then, move one square over, into the water, and set up another powerline parallel to the first. Repeat as needed, then bulldoze the powerlines to create new land. Another technique is to place a three lane highway over water. Then, repeat until there are three layers of three lane highway on top of each other. This will create a single section of land in the middle.