This actually started out as something completely different (a repeater that didn't function) but it turned out to make one of my favorite things: LOTS OF MIST!
slightly harder to build than my mini-generator, but not much bigger (unless you want it to be, see below) and can be built virtually anywhere, because it goes -above- the room where you want the mist
you build it, you pond-fill the one tile with water (then shut the pond zone off), and turn it on. it moves the block of water around the system in a loop, creating mist during the split second when it falls down into the room below (the next pump in the loop sucks it up before it can spread out).
the statues (or etc) aren't completely necessary, but it prevents dwarves from standing where the water lands (which can lead to annoying 'dangerous terrain' cancellation spam, but might be a plus if you want to wash your dwarves). statues also hide the 'muddy' floor tile below. (they don't get muddy themselves, which is cool)
you can also remove the walls where the original 'pond' was (and stick in another statue there), although this means you'll have to rebuild them if you ever want to turn it off and restart it again (Although i can't think why you would
You can also expand this design as much as you like, it just takes more power and more pumps (although it appears you can only have a maximum of 1 block of 7/7 water in the system. i tried starting it with two 6/7 blocks at opposite ends of the loop, and it overflowed the excess 5 water immediately). I just built an 8 pump version for a larger room, and my friend upon seeing it in action said "why not just build one of these that snakes around your entire fortress" to which i replied:
a video of the expanded version in action: http://mkv25.net/dfma/movie-1292-ubermistgenerator
[edit: i need to revamp this first post as the design has improved considerably (read the whole thread for the fleshing out), but in brief; the 'walled off pool' isn't necessary, you can fill the system after it's been turned on, nor are the statues (build paved road tiles out of blocks there instead, hides the mud and looks the same as a smoothed/built floor) also, your dwarves will learn swimming when they stand under the channels)