I would like to have a large underground room without it being either very dark or have light sources in the open (lava columns, torches). I use to build columns using stairs since they allowed light to pass through them, but this bug no longer seems to work.
Light will shine through paintings, but paintings have to be placed over solid blocks (which signs count as!), so you could make a wall like so:
##### ## ## #####
The hole in the middle would actually be 2 deep; you'd place a torch in the back, then a sign in front, then put a painting over the hole/sign; the torch would shine through the sign and painting, and light up the room (although the light would be somewhat diminished because the torch is recessed by 2 blocks).
STEP 1: STEP 2: STEP 3:
You could try these two methods of my own:
Raise the floor with stone slabs, and put glowstone around the bottom. Note: In newer versions of Minecraft, this no longer works. Since 1.4.2, half slabs block light from passing through them. So although you can see the lit glowstone (and smooth lighthing may cause the surrounding area to light up a bit), there isn't any "real" lighting going on, so the rest of the room will still remain dark, allowing for things such as mob spawning.
Hide glowstone in a location you can't see it, and let the light shine through glass. (This works well at the top and bottom of your room; my example shines through both the top, and bottom of the wooden wall, I just used water instead of glass on the bottom.)
Note: This is the piehole texture pack; the yellow stuff is glowstone.
You can dig a 2 deep trench in the floor, then place a glowstone block on the bottom. Once you place it, place a piston (either sticky or regular works) on top, and it'll give off the same amount of light as if the glowstone was above ground.
You can place jack-o-lanterns in the ground as well.
You could also place pressure plates (wooden or stone) over a jack-o-lantern that is in the ground. It doesn't have the most appealing look but it is hidden and gives off a lot of light.
Hope I helped!