To enter console commands, press "~" and type in "sv_cheats 1" in the command window. This will allow console commands to be entered. Please note that this will disable steam achievements.

Effect	Code
Activate/Disable Fly	noclip
Delete Zombies	remove_all npc_zombine
Disable Blood	violence_hblood 0
Disable HUD	hidehud 5
Disable Jump	sv_gravity_0
Earthquake	shake
Easy Mode	ai_disable
Enable Jump	sv_gravity_1000
Enable/Disable Edit Mode	editor_toggle
First Person Mode	firstperson
Freeze Corpses	cl_phys_timescale 0.0
God Mode	buddha
Kicks all Bots	bot_quota 0
Reenable HUD	cl_drawhud 1
Refill all Ammo	impulse 101
Spawn Airboat	ch_createairboat
Spawn Ammo	givecurrentammo (number)
Spawn Health	give item_healthkit
Spawn Jeep	ch_createjeep
Spawn Skull	impulse 102
Spawn Zombie	ent_create npc_zombine
Suicide	die
Third Person Mode	thirdperson