Doom 2

IDDQD      =INVINCIBILITY
IDKFA      =ALL GUNS ALL AMMO USE NO. KEYS TO GET THE DIFFERENT GUNS
IDCLIP     =WALK THROUGH WALLS
IDCLEV     =LEVEL--
IDFA       =ALL AMMO
IDCHOPPERS =CHAINSAW

Some Level Passcodes...
Level 40 : Refueling Base - WS58ZKCRKH
Level 41 : O of Destruction! - CSNRG2W820
Level 42 : The Factory - WT670JBQJG
Level 43 : The Inmost Dens - DQLTJ1Y!02
Level 44 : The Suburbs - 2N94VFFMFC
Level 45 : Tenements - CQLTJ0Y!02
Level 46 : The Courtyard - WR492GDSGJ
Level 47 : The Citadel - PFFGXH3777
Level 48 : Nirvana - JWCJV2X479
Level 49 : The Catacombs - CJJTM35964
Level 50 : Barrels Of Fun - M!T174XZXV
Level 51 : Bloodfalls - 5770MX2CDF
Level 52 : The Abandoned Mines - YJLW3PPCPM
Level 53 : Monster Condo - DKKBLM58J3
Level 54 : Redemption Denied - 7L3!266DJK