Hold SHIFT and type 'FUND' for $10,000.  It will cause an earthquake every 
third time you do it, so do it before you start your city. 
 
Another tip is to set the citizen's taxes to 0%.  Then just before tax 
collection (December or November if playing at fast speed) quickly set the 
taxes up to 20%.  Then after you collect taxes, put it back down to 0%. 
This way the citizens think they are not paying any taxes. 

Want $2 billion?  Try this:

         C:\> DEBUG   filename.CTY
              - E D24
              7F
              - E D25
              FF
              - W
              - Q
        
This will affect the year of your city.  No disasters will occur.