Red Alert's Command And Conquer

Hold Shift and type:
SHIFT+GOLD - 10000 credits
SHIFT+HEALTH - All units gets full health
SHIFT+DEATH - Invincibility

There's a little trick that allows you to build anywhere you like (NOTICE, this only works in some versions of the game).
It requires you to build a communication centre and at least one soldier.
Another tip would be to know the location of the enemy base by sending fast vehicles to corners of the map.
1: Activate a soldier and click the structure you want to build
2: Place the structure on top of one of your already build structures, which is of course not allowed.
3: Now you can place your structure almost anywhere you want, even in the enemy base (Guard towers might be a good example)