What is more ubiquitous in a dungeon than a floor? Whether it be made of wood, stone or dirt, almost all dungeons have floors, and other than the occasional pit, what adventurer ever pays much attention to the floor? Floors provide ample opportunities to spice up your dungeon, and it doesn't even have to be complex or convoluted, yet it can still be fresh and unexpected.
The wooden floor in this room is highly polished and clean.
Type: mechanical; Perception DC 16; Disable Device 22
Trigger touch; Reset None
The floor has been polished and waxed. Normal movement is not affected, however, any other actions, including spell casting with somatic components, combat actions or running are affected. Waxed Floor (DC 15 Acrobatics check or fall prone)
There is nothing tricky, fancy or even inherently deadly about this trap. However, whether or not the characters take precautions, such a simple little trap can add some flavor and take the difficulty up a notch. That charge that the fighter does is far less effective when he slips and falls, as is the mage when he falls down casting a fireball. If your dungeon denizens are immune to the effect, either through preparation of some other mechanism, this becomes even more devious. However, if they aren't ready, nothing spells fun and memories like 10 kobolds running into a room and all slipping and sliding like a 3 Stooges movie.
Finally, your players will know you care. How many GM's make sure that their dungeon floors are clean for their guests?