Press [Enter] during game play in single player mode:

Spawn Russian M80 Tank - motherrussia
Spawn CIA Armored SUV - coolihaveanewcar
Spawn S.W.A.T. member - swatatyourorders
Spawn British cop - greenjelly
Spawn SA12 Anti-Aircraft Missile Launcher - blackhawdown
Spawn Duck - duckhunt
Spawn U.S. police officer - ymca
Spawn President of The United States of America - coolimthepresident
Spawn British Ambulance - bringoutthedead
Additional $1,000 - fortknox
Full map - keyholemaster
Launch a super weapon (nuclear bomb) at the pointer - yeepeekaye
Unlimited money and entire tech tree unlocked - ineedalltechnos