idchoppers - chainsaw - long story behind the message idclevXY - warp - X is the episode number, Y is the level number. iddqd - Degreelessness mode - God Mode! idkfa - very happy ammo - full ammo and keys. iddt - toggles automap - 1x = full, 2x = full with objects. idmypos - displays bearings and coordinates - this is displayed in hex. idspispopd - no clipping mode - You can walk through walls. idbehold - Displays menu - type s, v, i, r, a, or l afterwards. list is below. S = Berserk - your punch is equivilant to a rocket, lasts 1 level. V = Invulnerability - temporarely invincible. I = Partial invisibility - your enemies can see you, barely! A = Computer Area Map - better than IDDT because parts you didn't visit are gray. R = Anti-Radiation suit - good for that green slime! L = Light Amplification visors - you can see in the dark!
Thanks to the Doom FAQ for helping me out.