Baldur's Gate

First, to activate the cheats, you have to edit the file baldur.ini in your Baldur's Gate directory and add the line "Cheats=1" under the [Game Options] area.

After you start the game, hit CTRL+TAB to bring up the console. (CTRL+TAB again closes the console). Type in the following cheats and hit [Enter] to activate each one. Before each cheat, you'll have to enter "Cheats:", so Cheats:Midas() would activate that cheat.

Midas(): Gives you 500 gold.
FirstAid(): Creates 5 healing potions, 5 neutralize poison potions, and a stone to flesh scroll.
CriticalItems(): Spawns all the game's critical items.
Hans(): Moves your character to a free adjacent area.
ExploreArea(): Marks entire area explored.
CowKill(): Creates CowKill spell if near a cow.
TheGreatGonzo(): Summons 10 killer chickens as allies.
DrizztAttacks(): Creates a hostile Drizzt.
DrizztDefends(): Creates a friendly Drizzt.

Battle Beast

To activate cheat codes, first type YOYOYO during gameplay, then enter the following codes:

ORUFO: Invincibility in bonus rooms
AOFREOIO: Open all bonus doors
EATEE: Morphing disabled
EHRTRR: Auto fly in bonus rooms
NHAENRH1: Unlimited ammo for player 1
NHAENRH2: Unlimited ammo for player 2
ERHYHRLY: Toadman weaker
OFOVH: Double the time in rooms
OIVNNFOF: Keeps tadpoles from attacking in lab
OAOAEIOA: Auto-fly mode in lab
ITIHFO: Best 2 out of 3; using this code will turn your bouts from the regular format

Betrayal in Antara

During the game, hit CTRL+SHIFT+Z, then type one of these codes:
some call me tim: kills all foes (in combat)
gotta have magic: gives Aren all spells
man does my leg hurt: heals party

Blood Shareware

To activate these codes, hit T during gameplay, then enter the code and press ENTER.

NOCAPINMYASS: God mode.
CAPINMYASS: God mode off.
EVA GALLI: Clipping on/off.
GOONIES: Full map.
RATE: Displays frame rate.
IDAHO: All weapons and ammo.
BUNZ: All weapons and ammo.
LARA CROFT: All weapons, unlimited ammo.
HONGKONG: All weapons, unlimited ammo.
MONTANA: All weapons, ammo, and items.
KEYMASTER: All keys.
SATCHEL: All items.
SPORK: 200 health.
CLARICE: 100 health.
GRISWOLD: Full armor.
ONERING: Toggles invisibility.
CALGON: Level skip.
MCGEE: Set yourself on fire.
FORK BROUSSARD: No weapons, 1 health, and drunk mode.
STERNO: Fade to black.
JOJO: Drunk mode.