I know the Konami code obviously... won't type it out as per request. Here's some others permanently engraved in my head.
NES:
The Legend of Zelda second quest: Name your character "ZELDA"
Metroid password (Samus with no suit): JUSTIN BAILEY ****** ******
GENESIS/SEGA CD:
Sonic the Hedgehog 1 level Select: Up, Down, Left, Right, A, Start.
Sonic the Hedgehog 2 level select: In Sound Test play 19, 65, 9, 17. Back at title, Hold A and press Start.
Mortal Kombat blood kode (Genesis): During introduction press A, B, A, C, A, B, B.
Mortal Kombat DULLARD cheat menu (Genesis): On title screen press Down, Up, Left, Left, A, Right, Down.
Mortal Kombat II Test Mode kode (Genesis): Highlight "Done!" in the Options menu and press Left, Down, Left, Right, Down, Right, Left, Left, Right, Right.
Shining Force II Secret Configuration Code: On SEGA logo quickly press Up, Down, Up, Down, Left, Right, Left, Right, Up, Right, Down, Left, Up, B.
Disney's Aladdin level skip (Genesis): Pause the game and hit A, B, B, A, A, B, B, A.
The Terminator level select (Sega CD): Highlight "Run Game." Hold down Left the hit B, C, B, C. Release Left and press A.
PC:
God Mode in Oblivion and Fallout 3: Hit Tilde key for cheat console and type "tgm"
Warcraft II Oil cheat: "valdez"
Warcraft II Gold cheat: "glittering prizes"
Warcraft II hidden song: "disco"
Starcraft map cheat: "black sheep wall"
Neverwinter Nights 2 debug: Hit Tilde key for cheat console and type "debugmode 1"
Neverwinter Nights 2 exp cheat: Hit Tilde key for cheat console and type "givexp #"
The Sims 2 money cheat: Press Ctrl + Shift + C for cheat console and type "motherlode"
The Sims 2 rotation cheat: Press Ctrl + Shift + C for cheat console and type "Allow45DegreeAngleOfRotation True"
A couple of those I had to look up as it has been a while since I had done them (The Aladdin and Terminator ones) but at the time, they were indeed imprinted in my head from overuse. Still counts in my book.
NES:
The Legend of Zelda second quest: Name your character "ZELDA"
Metroid password (Samus with no suit): JUSTIN BAILEY ****** ******
GENESIS/SEGA CD:
Sonic the Hedgehog 1 level Select: Up, Down, Left, Right, A, Start.
Sonic the Hedgehog 2 level select: In Sound Test play 19, 65, 9, 17. Back at title, Hold A and press Start.
Mortal Kombat blood kode (Genesis): During introduction press A, B, A, C, A, B, B.
Mortal Kombat DULLARD cheat menu (Genesis): On title screen press Down, Up, Left, Left, A, Right, Down.
Mortal Kombat II Test Mode kode (Genesis): Highlight "Done!" in the Options menu and press Left, Down, Left, Right, Down, Right, Left, Left, Right, Right.
Shining Force II Secret Configuration Code: On SEGA logo quickly press Up, Down, Up, Down, Left, Right, Left, Right, Up, Right, Down, Left, Up, B.
Disney's Aladdin level skip (Genesis): Pause the game and hit A, B, B, A, A, B, B, A.
The Terminator level select (Sega CD): Highlight "Run Game." Hold down Left the hit B, C, B, C. Release Left and press A.
PC:
God Mode in Oblivion and Fallout 3: Hit Tilde key for cheat console and type "tgm"
Warcraft II Oil cheat: "valdez"
Warcraft II Gold cheat: "glittering prizes"
Warcraft II hidden song: "disco"
Starcraft map cheat: "black sheep wall"
Neverwinter Nights 2 debug: Hit Tilde key for cheat console and type "debugmode 1"
Neverwinter Nights 2 exp cheat: Hit Tilde key for cheat console and type "givexp #"
The Sims 2 money cheat: Press Ctrl + Shift + C for cheat console and type "motherlode"
The Sims 2 rotation cheat: Press Ctrl + Shift + C for cheat console and type "Allow45DegreeAngleOfRotation True"
A couple of those I had to look up as it has been a while since I had done them (The Aladdin and Terminator ones) but at the time, they were indeed imprinted in my head from overuse. Still counts in my book.