Press Control+Alt+Tilde(~) To open the console, or just tilde if the com_allowconsole 1 cheat is typed in. The 'god' and 'notarget' codes are recommended before spawn a monster.

Spawns a Wraith demon - spawn monster_demon_wraith
Spawns a Fat2 zombie holding a wrench - spawn monster_zombie_fat_wrench
Spawns a Fat zombie with his intestines showing - spawn monster_zombie_fat2
Spawns a Jumpsuit zombie - spawn monster_zombie_jumpsuit
Spawns a bald "Yellow Jacket" zombie - spawn monster_zombie_maint_bald
Spawns a No Jaw "Yellow Jacket" zombie with a flashlight - spawn monster_zombie_maint_flashlight
Spawns a "Yellow Jacket" zombie with no jaw - spawn monster_zombie_maint_nojaw
Spawns a Skinny "Yellow Jacket" zombie - spawn monster_zombie_maint_skinny
Spawns a No Jaw "Yellow Jacket" zombie with a wrench - spawn monster_zombie_maint_wrench
Spawns a completely black "Yellow Jacket" zombie - spawn monster_zombie_maint2
Spawns a Chainsaw zombie - spawn monster_zombie_sawyer
Spawns a skinny zombie - spawn monster_zombie_skinny
Spawns a Suit zombie with a bloody mouth - spawn monster_zombie_suit_bloodymouth
Spawns a Suit zombie with no head - spawn monster_zombie_suit_neckstump
Spawns a Skinny Suit zombie - spawn monster_zombie_suit_skinny
Spawns a Bald zombie similar to the one in the infirmary - spawn monster_zombie_tshirt_bald
Spawns a zombie almost exactly like the one in the infirmary - spawn monster_zombie_tshirt_blown