This is a list of four-letter codes for each creature that can be summoned to either your hand or directly to the playing field. Enchantment and sorcery spells are not included in this list -- it is creatures only.
To use, hit the "~" key while in a battle to bring up the console. To activate cheats, type "EtherRevelation". To use these codes, enter one of the following, followed by a 4-character code. Not all codes have been tested yet. Thanks to CyberMan for initial information on using cheats. [NOTE: 4-character code MUST be in all caps or it will not work.]

add spell <4-char code> => Instantly adds spell to your hand. Ex: 'add spell TIWR'

add creature <4-char code> => Instantly adds creature directly to battle. Ex: 'add creature TIWR'

ANTN Ancient Treant
AREL Air Elemental
AVAS Aviak Assassin
AVEL Aviak Elder
AVMK Aviak Marksman
AVSC Aviak Scout
BATT Bat
BEHD Evil Eye
BEQN Bee Queen
BEWK Bee Worker
BEWR Bee Warrior
BGVL Big Velos
BHMO Evil Eye Mother
BHWR Evil Eye Warrior
BLDG Black Dragon
BRAB Bronze Abomination
BRMC Bronze Mechos
BRMZ Bronze Mechozaurus
BUDG Blue Dragon
CAFG Carnivorous Fingus
CCLP Cyclops
CLSP Cleric Spirit
CTMN Cutter Man
DMRT Doom Rat
DRAT Disease Rat
EREL Earth Elemental
FMFI Female Fighter
FREL Fire Elemental
GBAT Giant Bat
GBBR Gibberling
GBGN Gibberling Gang
GBIN Gibberling Instigator
GIFG Giant Fingus
GRDG Green Dragon
GRFG Gargantuan Fingus
GROG Gray Ogre
GRSN Grass Snake
GRTN Great Treant
HOPR Hopper
IRAB Iron Abomination
IRMC Iron Mechos
IRMZ Iron Mechozaurus
KBEL Kobold Elder
KBGD Kobold Guard
KBSH Kobold Shaman
KBWR Kobold Warrior
LASN Lake Snake
LMMN Lamia Monk
LMWA Lamia Warrior
LMWD Lamia Warlord
LMWK Lamia Warlock
MAHO Magic Hornet
MCWO Mech Worm
MCWU Mech Wurm
MCWY Mech Wyrm
MLF I Male Fighter
MNHP Mini Hopper
MNTS Mantis
MOBE Mother Bee
MOTI Mother Tick
MTPT Mantis Patriarch
MTSC Mantis Scribe
MXHP Maxi Hopper
MYHO Mystic Hornet
NWLF Night Wolf
OGKN Ogre King
OREL Orc Elder
ORGD Orc Guard
ORSH Orc Shaman
ORWR Orc Warrior
PHWL Phantasmal Wall
PRAT Plague Rat
PTRS Pteros
RDDG Red Dragon
RFPT Reinforced Pteros
RKWL Rock Wall
RVHL River Halo
RZMN Razor Man
SEHL Sea Halo
SHSP Shaman Spirit
SHWL Shadow Wolf
SLWL Silicon Wall
SMVL Small Velos
SPFG Spitting Fingus
STAB Steel Abomination
STMC Steel Mechos
STMZ Steel Mechozaurus
STRT Stink Rat
SWHL Swamp Halo
SWMN Sawer Man
SWSN Swamp Snake
TANT Treant
TIQN Tick Queen
TIWK Tick Worker
TIWR Tick Warrior
TNSA Treant Sapling
TRSN Tree Snake
VBAT Vampire Bat
WKHR Walking Horror
WLAR Wall of Air
WLBL Wall of Blades
WLBR Wall of Burning Rock
WLBZ Wall of Breeze
WLDG Wall of Daggers
WLDT Wall of Distortion
WLFC Wall of Force
WLIF Wall of Inferno Flames
WLIL Wall of Illusion
WLLV Wall of Lava
WLMG Wall of Magma
WLWD Wall of Wind
WRSP Warrior Spirit
WTEL Water Elemental
WZSP Wizard Spirit