Hidden and Dangerous

Demo version cheats:
In the demo, type unlockcheatmode on the "Choose Campaign" screen after the intro. A click confirms it. Then type one of these during play or at any menu:
zombie        Come back as a zombie after being killed
bighead       Big head mode
killthemall   Kill all enemies
showtheend    See the ending
missiondone   Win the current mission
missionfail   Lose the current mission
openalldoor   Open all doors
allammo       All weapons and ammo
laracroft     Different uniforms
enemylookf    View of the enemy in front
enemylookb    View of the enemy behind
playercoords  Show your coordinates in the upper left corner

Anthony Switcher:
With 100 stealth, Anthony Switcher gets the drop on most enemies before they see him. Give him a sniper rifle and he can clear most night missions almost on his own.

Let the computer shoot and throw:
Leave soldiers with high shooting skill (e.g. Robin "Hood" Smedley and Tony Atkins) on computer control in combat.
To throw a grenade, command the soldier on the map screen and pick the target: the computer judges the distance better than you can.

Erase old commands:
Backed-up commands cause strange behaviour that looks like bugs, so erase old commands when you plan a battle on the map view.