Sometimes the adventurers are heading down a long, dark (somewhat boring) corridor and you want to give them some details to spice it up (and increase their unease and paranoia!)
Here's a quick table that I put together for just that purpose. Roll a d10 to select a random element. Most of them have another d6 subtable built in for more random goodness. :)
If anyone is inspired by the list and would like to add additional ideas in the comments, I'll collect everyone's ideas and turn them into a PDF file for download.
1 - Strange chalk markings are scratched on the walls and floor (d6: 1 - measurements; 2 - message; 3 - wizard marks; 4 - mystical runes; 5 - warning; 6 - gibberish)
2 - Footprints (d6: 1 - boots, 2 - reptilian, 3 - feline, 4 - lupine, 5 - ursine, 6 - strange) lead away from the party and are just barely visible in the dust.
3 - The floor stones are loose and wiggle when stepped upon.
4 - Periodically, steam rises up from cracks in the floor.
5 - The floor is covered with a few inches of water. (d6: 1 - it bubbles; 2 - it smells foul; 3 - its warm; 4 - its uncomfortably hot; 5 - it is icy cold; 6 - it is acidic and begins to dissolve footwear)
6 - Dozens of spikes are driven into the walls and remnants of rope are attached to some.
7 - The walls are carved in bas relief (d6: 1 - mouths; 2 - eyes; 3 - snakes; 4 - geometric patterns; 5 - abstract humanoids; 6 - tentacled horrors)
8 - The walls are covered in murals of (d6: 1 - a battle; 2 - a ritual; 3 - a pleasant scene; 4 - an abstract scene; 5 - a godly visage; 6 - a dark visage) that are in (d4: 1 - well maintained; 2 - aged but well preserved; 3 - ruined; 4 - barely understandable) condition.
9 - A trap (d6: 1 - blades; 2 - falling blocks; 3 - moving walls; 4 - pits; 5 - spears; 6 - chute/slide) has been triggered and has not been reset. It may have victims...
10 - The walls and floor (d6: 1 - change material; 2 - are oddly unfinished; 3 - are covered in blood; 4 - appear to be made of flesh; 5 - arc with energy; 6 - are vibrating).