I worked at the Beverly office a while back, and these are what just comes to mind.
NWN1: Pretty close to release, and within my first week there i noticed that you could drop gold on the ground but it wouldnt subtract from your inventory.
NWN1: For a long time you could reject your level up roll for HP if you didnt get a 20.
NWN1: Most go get this or that quests are repeatable if you drop the item in question just before saying here it is. then you pick it up and talk again.
Moonbase Commander: On one level you were attacked by three AI. Two would attack randomly, the third would always attack in the same spot in the same amount of turns. So once you got the shot correct, you could always stop that AI.
Unreal2: For a long time the AI of the vicious pig looking monters was broken in that they wouldnt actually attack you, but rush and growl. Most people would always just blow em away anyways so it was barely noticed.
Unreal2: There was a bug where randomly if you used a sniper rifle on your enemy, the ragdolled corpse might fall to the ground then twitch, and then fling off into the direction of the push from the force of impact. Was funny to see a corpse just hit the ground then skid across the map.
UnrealT2k3: The link gun use to not lose power from a teamate when he was killed. So you could raise the power of the gun to the point where it pushed the person firing it into a wall with enough force to kill them. Also one could aim at the groind and fly into the air and get crushed against the skybox.
UnrealT2k3: I forget the map but there was a spot on a CTF map where either blue or red side could take the opposite flag and hide in a rock near thier own. I actually saw this a year after release when i saw kids playing the map in a lan event. Didnt tell them about it.
Ahh good times.