Three years ago when I started playing DDO, I came from WoW and it's many many clones. I went through korthos and saw the puzzles and was slightly impressed that the dungeon was more immersive than a "long bendy hallway full of mobs with a few bosses interspersed" that was wow and all it's clones. Then I got to my first trap and my reaction was "OMG the dungeon itself can kill you, this is awesome!" That was the moment I truly fell in love with DDO as a game. Thinking back to the first time I ran into many surprises and traps, I started thinking about which one was the most awesome.
The conclusion I came to was that it was this one trap in monastary of the scorpion. You fall through a puzzle floor just before you complete it and land in water. There is a chest behind a secret door down there. To get back up you have to activate a blower that sends you back up through the air so you can land in the doorway up there. The catch: The blower is keeping several, nearly invisible, gelatinous cubes suspended in the air and will blow you through them repeatedly till you die. I think it is the cleverest and most imaginative trap for a dungeon and it reminds me of many good ol' PnP dungeons.
My second favorite trap was the greased slope with spikes at the bottom underneath a breakaway floor in Rainbow in the Dark. It was multiple traps elements working together to make a pretty effective trap, and there was no surviving if you were not prepared for it. Very effective against the unwary.
Those traps were downright interesting. We need more things like that in DDO. Spikes, blades, elemental blasty thingies, and spell wards are fine and all, but we need more traps with some imagination in them. When I die in a trap I want to be imagining some evil genius cackling maniacally in evil glee because no one could have seen that coming. Most traps though, they seem more like some evil random guy is sitting at a monitor thinking, "Really, I can't believe this got anyone at all, how did you even die in it?"
Maybe the devs could have a contest and have the top five winners get to have a trap of their own design included in the following update's content. Or something along those lines. I know a lot of people who would love to be able to do something like that.