Overkill, overpowered, TPK traps are fun to have in your dungeon, provided they don't actually kill anyone. For example:
Golden Ball Trap
A huge golden ball, warm to the touch, sits in a depression atop a raised dais that has stairs all around. The ball is full of molten gold. If the ball is touched, the thin, solid outer wall breaches, spilling molten gold into the room. Once emptied, the gold can be scraped off the floor and would be quite valuable once it is solid.
Very Hard Perception, or Hard Alchemy or Dungeoneering check.
Very Hard Reflex Save or everyone in room takes APL * d6 fire damage. Each round each character takes APL * d6 fire damage on his turn if he is in the molten gold at any time during his turn. If he is flying or otherwise not touching the floor, the damage is APL * d3. The gold stays molten for 2 * APL rounds.
This is a very deadly trap. It is also very obvious. Therefore, you may ask, "What is the value of having such an obvious trap in my dungeon?"
The answer is simply the joy of overcoming such a huge obstacle and enjoying the spectacle of it. There in an inherent "wow" factor in avoiding or disarming such a deadly trap. It sends a message that you, as a GM don't mess around, and also gives the characters a feeling of accomplishment in avoiding your attempt at killing them.
Plus, with this one, you present them with the quandary of how to remove so much treasure.