Thank you! Last year they liked the 'mist' setting on the hose, so I will go look for a small, misty-type sprinkler. We have a larger aviary under construction, so hopefully we can get all of this worked out in the next month or so. I just went out and dumped/refilled their pools, and hosed down the entire area (oooo, mom made mud!). Since we are expecting rain in another hour, that should hold them... they are both happily pool splashing.
I like the ice idea as well. One of my silly problems is that my larger Pekin, the one who is most hot, HATES a dirty pool. So while I don't mind refilling every day, that is going to be an added chore. I could get away with three-four days when it was cooler. My smaller one doesn't care, as long as it's water.
We have a huge sprinkler/waterer out in our pasture for the horses. Now I get to relay to DH that we need a duck sprinkler! 
Anyone else? What do you do to keep your ducks cool in this nasty, muggy heat? As we get this aviary underway, I would love to see/hear ideas.
I keep thinking of the misters at amusement parks! 
Keep the ideas/pics coming.... thanks everyone!