X-Com: UFO Defense
The governments really don't care if you don't go to ground battles. If you just watch the world and shoot everything down they will continue uping your paycheck. After about ten months you should be getting about $10,000,000 from the U.S.A. alone!
To make fast cash, research an item and then manufacture it -- without specifying the number of technicians on payroll and the production goal. Go to the main menu and return, entering the number of employees on the payroll and a production goal of one unit. The item will be manufactured free of charge, making its sale a profit!
Scientists Work For Free
At the end of the month, before you the monthly rating. Transfer all personal(Scientists, Engineers, and Soldiers) While they are being transported the are not accounted for in the monthly expenses.