Cheat mode:
Start the game with the +set console 1 command line parameter. Press ~ to display the console, then enter cheats 1 to enable cheat mode:

Result - Code:

Extra ammo - updateinvfinal
Slow motion - matrix (1-10)
Level select - map (level name)
Spawn indicated object - gimme (item name)
Suicide - kill
God mode - heretic
No clipping mode - phantom
Invisible to enemies - ninja
Kill all enemies - killallmonsters
First six weapons with ammo - elbow
Last six weapons with ammo - bigelbow
Return to default weapons - defaultweapons

Level names:
Use one of the following level names with the map code.

Level - Name:

New York - trs1
South Africa - trn1
Shop - arn1
Kosovo (Tunnel system) - kos1
Kosovo (Town) - kos2
Kosovo (Helipad) - kos3
Siberia (Snow) - sib1
Siberia (Fortress) - sib2
Siberia (Rocket launching site) - sib3
Baghdad (Town) - irq1a
Baghdad (Warehouse) - irq2a
Baghdad (Airport) - irq3a
Shop - arn2
New York (Warehouses) - nyc1
New York (Tunnel system) - nyc2
New York (Hotel) - nyc3
Sudan (Train station) - sud1
Sudan (Slaughter house) - sud2
Sudan (Underground) - sud3
Shop - trm3
Tokyo (Restaurant) - jpn1
Tokyo (Sumi) - jpn2
Tokyo (Penthouse) - jpn3
Baghdad (Town) - irq1b
Baghdad (Palace) - irq2b
Basra - irq3b
Hanover (Fortress) - ger1
Hanover (Secret doors) - ger2
Hanover (Rocket launching site) - ger3
End - ger4

Item names:
Use the following steps to view all items names that can be used with gimme code. Enter developer 1 at the console window, then enter entlist to display a list of items and objects that can be used with the "Spawn indicated object" code. Some names include the following:

Item: Name:

Knife: item_ammo_knife
9mm Black Panther: item_weapon_pistol1
.44 Silver Talon: item_weapon_pistol2
Berzerker Shotgun: item_weapon_shotgun
Raptor Submachinegun: item_weapon_assault_rifle
EagleEye Sniper Rifle: item_weapon_sniper_rifle
Bulldog Suppressed machine gun: item_weapon_machinepistol
Slugthrower: item_weapon_autoshotgun
Heavy Machinegun: item_weapon_machinegun
Rocket Launcher: item_weapon_rocketlauncher
Flamegun: item_weapon_flamethrower
Microwave Pulse Gun: item_weapon_microwavepulse
Ballistic Armor: item_equip_armor
Flash Pak: item_equip_flashpack
Neural Pulse Emitter: item_equip_neural_grenade
C4/Plastique: item_equip_c4
Angel Light Goggles: item_equip_light_goggles
Medkit: item_equip_medkit
Frag Grenade: item_equip_grenade
Throwing Knives: item_ammo_knife
9mm Ammo: item_ammo_pistol
Shotgun Rounds: item_ammo_shotgun
.44 Pistol Ammo: item_ammo_pistol2
5.56 Ammo: item_ammo_auto
MPG Ammo: item_ammo_battery
Flamegun Ammo: item_ammo_gas
Rocket Launcher Rockets: item_ammo_rocket
Slugthrower Ammo: item_ammo_slug