Console Codes:
Use the [~] key during gameplay to bring up the console and enter the following codes there:

physcannon_cone # - Changes the radius of the cone used to pick up objects
physcannon_tracelength # - Changes the length that objects can be pulled from
physcannon_maxmass # - Changes how large pulled objects can be
physcannon_pullforce # - Changes how quickly objects are pulled
physcannon_maxforce # - Changes how hard you propel objects
God - God Mode (Server side only)
sv_soundemitter_filecheck - Toggle reporting missing .wav files for sounds
mat_numtextureunits # - Limit the number of texture units. (Add number in place of #) (0=Default)
sv_maxvelocity # - Sets Maximum Velocity of any moving object (Add number in place of #)
sv_waterdist # - Set Vertical View when eyes are near water plane.
air_density # - Change the density of air. (Add number in place of #)
dsp_explosion_effect_duration # - Set length of confusion/ear-ringing effect(Add number in place of #)
prop_debug - Toggle bounding-boxes debug mode on/off red - ignore damage, white - respond to damage, green - health)
picker - Toggles Picker mode on
setpos - Move player to specified origin
sv_bounce # - Sets bounce multiplier for physically simulated object collisions
npc_create - Creates an NPC
npc_create_aimed - Creates an NPC (Aiming away from player)
cl_showfps 1 - Shows FPS Rate
sv_friction # - Set World Friction (Add number in place of #)
sv_stopspeed # - Set Minimum Stopping Speed on ground (Add number in place of #)
sv_gravity # - Set Gravity (Add number in place of #)
setang - Snap players eyes to a specified pitch
yaw cl_drawhud 1 - Toggle HUD display On
cl_enablehud 1 - Toggle HUD display On
Map # - Load Map (Input title in place of #)
Developer # - Sets developer mode to on/off/verbose (0-off, 1-on, 2-verbose)
+mlook - Enables mouse look
exec # - Execute a script file (Input filename in place of #)
viewmodel_fov # - Adjusts size of the weapon you're carrying (54 = default)
give # - Give weapon (Input weapon name in place of #)
hud_quickhelp/text? 1 - Shows Crosshairs
maps - Displays Map listing
noclip - Ability to walk through walls (Server Side Only)
notarget - Invisible to NPC's
impulse 82 - Spawn a Jeep
impulse 101 - All Weapons
Hurtme # - Damages player by whatever variable you input as #
buddha - Health never goes below 1
impulse 76 - Grunt-O-Matic
give weapon_shotgun - Recieve a Shotgun thirdperson
Third Person - View firstperson
First Person - View
sv_cheats 1 - Activates Cheats
crosshair 0 - Disables Crosshair
sk_npc_dmg_shotgun # - NPC's do # damage with shotgun
sk_npc_dmg_smg1 # - NPC's do # damage with the smg
sk_npc_dmg_ar2 # - NPC's do # damage with the pulse rifle
mat_depthbias_normal 1 - See through walls
give weapon_annabelle - gives you Father Gregori's modified shotgun
ai_disable - toggles enemy AI on/off
sv_infinite_aux_power 1 - gives infinite power for sprinting, etc.
impulse 203 - removes the item or NPC pointed at
mat_fullbright 1 - removes all shadows (a 0 restores them)
skill # - change skill level (# = 1, 2, or 3)
status - shows some game info, incl. current map
help $ replace $ with a command to get a brief description of it
sk_max_357 # # is new max ammo for .357 Magnum
sk_max_ar2 # # is new max ammo for Pulse Rifle
sk_max_ar2_altfire # # is new max ammo for Pulse Rifle energy orbs
sk_max_buckshot # # is new max ammo for shotgun
sk_max_crossbow # # is new max ammo for crossbow
sk_max_grenade # # is new max ammo for hand grenades
sk_max_pistol # # is new max ammo for pistol
sk_max_rpg_round # # is new max ammo for RPG
sk_max_smg1 # # is new max ammo for submachine gun
sk_max_smg1_grenade # # is new max ammo for SMG grenades
sv_unlockedchapters # unlocks chapters 1 thru # (15 is end credits)
sk_plr_dmg_pistol # # is new damage value for pistol
sk_plr_dmg_357 # # is new damage value for .357 Magnum
sk_plr_dmg_ar2 # # is new damage value for Pulse Rifle
sk_max_smg1 # # is new max ammo for submachine gun
impulse 203 - removes the item or NPC pointed at
mat_fullbright 1 - removes all shadows (a 0 restores them)
sv_infinite_aux_power 1 gives infinite power for sprinting, etc.
cl_showpos 1 - brings up position display in top right of screen (0 removes it)
getpos - can be used to get current coords for use with setpos
sk_plr_dmg_smg1_grenade # # is new damage value for SMG grenades
sk_plr_dmg_smg1 # # is new damage value for submachine gun
sk_plr_dmg_rpg_round # # is new damage value for RPG rockets
sk_plr_dmg_grenade # # is new damage value for grenades
sk_plr_dmg_crowbar # # is new damage value for crowbar
sk_plr_dmg_crossbow # # is new damage value for crossbow
sk_plr_dmg_buckshot # # is new damage value for shotgun
net_graph 1 a more thorough fps display
impulse 83 - Spawn an Air Boat
cl_ragdoll_collide 1 - Enables ragdolls that don't clip through each other, but stack realistically on one another.
weapon_smg1 Submachine Gun
weapon_shotgun 12-Gauge Shotgun
weapon_rpg Rocket-Propelled Grenade Launcher
weapon_pistol 9mm Pistol
weapon_physcannon Zero Point Energy Field Manipulator Gun
weapon_crowbar Crowbar
weapon_frag Fragmentation Grenade
weapon_crossbow Crossbow
weapon_ar2 Overwatch Standard Issue Pulse Rifle
weapon_bugbait Pherapods
weapon_357 .357 Magnum
sk_plr_dmg_buckshot # Raises damage done by each pellet.
sk_max_buckshot # Raises your max number of shells to that number.
sk_plr_num_shotgun_pellets # Increases pellets fired from each shotgun shell. 100 works well. 1000+ and it lags.
give item_battery - Increases suit charge by 15 points.
give item_box_mrounds - Spawns primary fire ammo for the submachinegun
give item_ammo_crossbow - Spawns ammo for the crossbow
give item_ammo_357 - Spawns ammo for the .357 magnum
give item_box_srounds - Spawns ammo for the 9mm pistol
give item_rpg_round OR give item_ml_grenade - Spawns grenades for the RPG
give item_ar2_grenade - Spawns grenades for the submachinegun, oddly enough..........
give item_ammo_ar2 - Spawns primary fire ammo for the Overwatch Pulse Rifle
give item_box_buckshot - Spawns shells for the 12-gauge shotgun
give item_ammo_ar2_altfire - Spawns energy grenade for the Overwatch Pulse Rifle
mat_yuv 1 black-and-white mode
host_timescale # Changes the speed of the game (for slow-mo/fast-mo) (# < 1 = slower, # > 1 = faster).
ch_createjeep Make a jeep
ch_createairboat Makes an airboat
Kill - You die.

Console Code:
Open the console menu using ~ and imput this code:

bind key command

This binds a console command to a key. Note that if the command has arguments, quotes must be used. For example: bind x "impulse 101"

Be careful on which key you choose. If you use a key already in use for the game (W, A, S, D are for movement, 1-6 is used for weapons, G is for gravity gun, etc), the bind command will override the original command, and you will not be able to use it anymore.

How to Spawn NPCs:
Access the console, type in "npc_create npc_" and replace the name with one of these:

cscanner
rollermine
poisonzombie
mossman
monk
metropolice
manhack
launcher
kleiner
ichthyosaur
headcrab_poison
headcrab_black
headcrab_fast
headcrab
helicopter
gman
fastzombie
eli
dog
pigeon
seagull
crow
combine_s
combinegunship
combinedropship
citizen
breen
barney
barnacle
antlion
alyx
antlionguard
stalker
strider
vortigaunt
zombie
zombie_torso

Map codes:
Enter these with the 'map' code in the console. Press ~ to activate the console.

d3_c17_01 - Spawns you in the city 17 rebellion
d2_prison_01 - Spawns you in Nova Prospekt
d2_coast_01 - Spawns you on the coast (Vehicle)
d1_under_01 - Spawns you in lab
d1_trainstation_01 - Spawns you in train station
d1_town_01 - Spawns you in Ravenholm
d1_canals_01 - Spawns you in the canals.

Weapon cheats:
To spawn armor, ammo, weapons, or any items of the nature, first open the console. Then type the following command: give"weapon entity" In place where weapon entity is, you input one of the codes below. The Organic Manipulator cannot be spawned because the map chooses whether or not it is organic. Refer to another cheat for that weapon.

weapon_shotgun - Shotgun
weapon_smg1 - MP7 with grenade launcher
weapon_rpg - Rocket Launcher
weapon_physcannon - The Manipulator
weapon_crowbar - Gordon's classic
item_dynamic_resupply - Fragmentation Grenade
weapon_crossbow - Crossbow
weapon_bugbait - Bug Bait (from Antlion Guards)
weapon_ar2 - Overwatch Standard Issue Pusle-Rifle
weapon_pistol - Pistol
weapon_357 357 - Magnum Revolver

Slow Deaths:
Open the console while playing the game, enter cl_phys_timescale 0.05 or any of the others listed below. (1 sets the game back to normal speed)

0.05 slow
0.5 mid-slow
0.1 super-slow
0.0 stop time

Obtain and use the Super Gravity Gun in early levels:
You must have sv_cheats 1 and access to the console for this to work. Enter the following commands in the console in order:

changelevel d1_trainstation_01 Switches you to the first level, replace d1_trainstation_01 with other

map names if you want map d3_citadel_04 Changes you to a level where you start with the super gravity gun

give weapon_physcannon Gives you the gravity gun again

Console Commands:
Use the [~] key during gameplay to bring up the console and enter the following commands there:

stop Stops recording the current demo.

record demo_name Records a demo of all the user's actions within the game until the "stop" command is issued.

play demo_name Plays demo.(change demo_name to the demo you want to be played)

'Alyx Gun':
Enter these codes in the console to get the 'Alyx Gun', which appears to be some kind of prototype pistol. Goes as the a third pistol, has 30 bullet clip, no extra ammo, and it looks like an iron bar that was surgically put into Gordon's side.

give weapon_alyxgun Gives you the 'Alyx Gun'
sk_plr_dmg_alyxgun # # is new damage for Alyx Gun (default 150
sk_max_alyxgun # # is new max ammo for Alyx Gun (default 0)