When you are playing in noclip-mode, then type 1_Chicken_2 Now you are a chicken!! (You are very small when you are a chicken)
Sent in by Andrea

/impulse 101- all weapons & ammo
/impulse 102- spawns giblets & blood
/impulse 103- shows monster stats while looking at monster
/impulse 104- list global entities
/impulse 105- silent player
/impulse 106- model /sprite stats, while looking at target
/impulse 107- texture name, while looking at object
/impulse 195- AI mode on
/impulse 203- delete monster or NPC from world
developer 1 - developer mode on
developer 2 - verbose developer mode
developer 0 - developer mode off
Sent in by Anon

TO CHANGE YOUR APPEARANCE WHILE PLAYING, TYPE THIS IN THE CONSOLE:

BIND W "+FORWARD;MODEL SAS"
BIND MOUSE1 "+ATTACK;MODEL ARTIC"
Sent in by MASTER ENYE

Type Brightness in console when you have activated the console hl.exe thing then,
This will get your game to be brighter. Another cheat to get you game brighter is
lambert -1.01 Its the best cheat. Gamma will also help too.
Sent in by Haidar Elmasri

You must follow the following directions to get these cheats to work
1. Start Half-life Using The Command Line "Hl.exe -console". You Can Now Access The Console Using The "~" Key.
2. Enter The Command "Sv_cheats 1" In The Console. Cheats Are Now Enabled.
3. Here's A Partial List Of Cheats.
/impulse 101
/God - Godmode (Invincibility).
/God 0 - Godmode off
/Noclip - No Clipping (Walk Through Walls, Etc.)
/notarget - Opponents
/Map C#A# - Go To Any Map. Entered In The Form C1a1, C1a2, Etc.
/Give Xxxx - Gives Any Item. In Place Of "Xxxx", Fill In One Of The Following:
Item_airtank
Item_antidote
Item_battery
Item_healthkit
Item_longjump
Item_security
Item_sodacan
Item_suit
Ammo_357
Ammo_9mmar
Ammo_9mmbox
Ammo_9mmclip
Ammo_argrenades
Ammo_buckshot
Ammo_crossbow
Ammo_egonclip
Ammo_gaussclip
Ammo_glockclip
Ammo_mp5clip
Ammo_mp5grenades
Ammo_rpgclip
Weapon_357
Weapon_9mmar
Weapon_9mmhandgun
Weapon_crossbow
Weapon_crowbar
Weapon_egon
Weapon_gauss
Weapon_glock
Weapon_handgrenade
Weapon_hornetgun
Weapon_mp5
Weapon_python
Weapon_rpg
Weapon_satchel
Weapon_shotgun
Weapon_snark
Weapon_tripmine
Map Cheat Codes
/MAP xxxx - go to this map name directly, where "xxxx" is the name of the map:
Single Player Maps
c0a0 c2a1 c3a1
c0a0a c2a1a c3a1a
c0a0b c2a1b c3a1b
c0a0c c2a2 c3a2
c0a0d c2a2a c3a2a
c0a0e c2a2b1 c3a2b
c1a0 c2a2b2 c3a2c
c1a0a c2a2c c3a2d
c1a0b c2a2d c3a2e
c1a0c c2a2e c3a2f
c1a0d c2a2f c4a1
c1a0e c2a2g c4a1a
c1a1 c2a2h c4a1b
c1a1a c2a3 c4a1c
c1a1b c2a3a c4a1d
c1a1c c2a3b c4a1e
c1a1d c2a3c c4a1f
c1a1f c2a3d c4a2
c1a2 c2a3e c4a2a
c1a2a c2a4 c4a2b
c1a2b c2a4a c4a3
c1a2c c2a4b c5a1
c1a2d c2a4c
c1a3 c2a4d
c1a3a c2a4e
c1a3b c2a4f
c1a3c c2a4g
c1a3d c2a5
c1a4 c2a5a
c1a4b c2a5b
c1a4d c2a5c
c1a4e c2a5d
c1a4f c2a5e
c1a4g c2a5f
c1a4i c2a5g
c1a4j c2a5w
c1a4k c2a5x
Multiplayer/Deathmatch Maps
boot_camp snark_pit
bounce stalkyard
datacore subtransit
lambda_bunker undertow
Hazard Course
t0a0 t0a0b2
t0a0a t0a0c
t0a0b t0a0d
t0a0b1
Please note: Some items may not be available in some areas.
Also, If you are using NOCLIP mode and shoot at the floor, you might just end up stuck in walls, between levels, and really lost.
Camera Changes
This is cool! Call up the console by pressing the ~ button and type any of these. They do all sorts of camera things:
"chase_active 1" - puts the camera on "Tomb Raider Mode"
"thirdperson" - Puts the camera in a "Third Person Mode" where the next 2 codes are useful.
"+cammouseactive" - activates "Camera Looking Around Mode" which can change your view in "Third Person Mode"
"-cammouseactive" - deactivates "Camera Looking Around Mode"
"chase_active 0" - deactivates "Tomb Raider Mode"
"firstperson" - returns you to "First Person" mode.
Sent in by Danny Jestin

start the game with the command line 'hl.exe -console' then in single player game access console with the ',' key (to the left of the '1') and type:
give weapon_[select weapon](e.g. 'rpg','357','crossbow',etc)
give item_[select item] (e.g. 'battery','suit','healthkit',etc)
Sent in by BEN ARTHUR FROM COTTINGHAM, ENGLAND

if your playing a tfc{team fortress classic} game in multipalyer on your half life game click on the console{~`} the button before # 1} and then type give tf_weapon_
after u type weapon_ put in your favorite gun from any class like soldier's gun is called rpg,hw is an ac and so on. so u would type give tf_weapon_ac
Sent in by Paul Dempsey