Weapon Select.
This must be done on the server machine. Type sv_cheats 1 at the console. Change the map with the changelevel <map name> console command. Then, type tf_weapon_<weapon name> at the console on any machine connected to the server to select that weapon.

Change gravity.
This must be done on the server machine. Type sv_cheats 1 at the console, then type sv_gravity<-9999-9999>.

Weapon Names.
Use one of the following entries with the tf_weapon_ code.

Item - Weapon name
Auto cannon - ac
Rocket launcher - rpg
Medic kit - medikit
Knife - knife
Super shotgun - supershotgun
Flame thrower - flamethrower
Railgun - railgun
Remote pipe bomb - pl
Grenade launcher - gl
Wrench - spanner

Snipe Further.
When playing a sniper type fov 10 at the console to double your sniping vision.

Shoot With Crowbar.
Use the following steps to use the crowbar to shoot bullets from the chaingun or flame from a pyro. Change your class to an HW or Pyro. Then, use up all your ammo from your chaingun or flamethrower. After wasting all the ammo, get out the crowbar and hold the Right Mouse Button (or whatever displays your special ability menu) and run over a pack of ammo. You should now be able to shoot with your crowbar.

Select crowbar, then select the weapon you want to shoot. Use all of the ammo and hold the button. While holding it, press Q twice. While still holding it, get a pack of ammo. Release the button and you will be able to shoot with your crowbar.

Dead Scout Sliding on the Ground.
Change your class to a scout. Go in the console, type +reload, then go underwater in any level. Go in the console and type kill. Wait for someone to get your pack, then you will be a zombie. To respawn again, go in the console and type -reload. Note: This trick has been disabled in the latest versions of the game.

Keep Same Number of Rounds After Switching Weapons.
Start a multi-player game and get the heavy weapons character. Have your Gatlin Gun ready and get ready to switch your gun. Have the gun that you want, ready then hold the Left Mouse Button for three seconds. You will hear the gun rotate. The gun you selected will have the same ammo that the other gun. This also gives you an extra 192 shots with the shotguns.

Invisible Spy.
While in Team Fortress Classic, become a spy. Press [Ctrl] to crouch. Press [Right Click] (special ability) and select "Feign". If done correctly, you will have feigned like normal, but instead of being on the surface, you are now under it and are not visible by any other players. Once you want to get out of this position, just stop "Feign". Note: This is a good trick to do in an enemy's base, as you are able to communicate with your team. This is also a good time to change disguises, while no one can see you.