I have a few different animals at the moment, and I would like to share a few ideas I have had that over the years that have proven to help them keep cool.
For the Guinea pigs we have discovered a cheep and easy solution. Old juice pop tops with frozen water in them. They freeze and wash easily, are reusable and our Guinea pigs simply lay across them to keep cool. For rabbits, I recommend coke or lemonade bottles as they are larger. they also take longer to defrost. I also move their cages into the shade, a well ventilated veranda is ideal, just make sure it's in the shade for the whole day.
My ducks and chickens have trees and a pond to cool off in, but they really appreciate a sprinkler on them during the hottest part of the day. It cools the whole atmosphere under the trees and wets the ground which they then dig holes and sleep in. The cool damp dirt keeping their body temperature down. If they are in a shed the same applies. The water cools the tin,and the temperature inside .
My dog lives inside on extreme days if we are home, but if I do need to work, I make sure he has several water supplies around the yard. We also keep the water cool by putting a large frozen ice block in the water, usually made by freezing water in a margarine container. As he is a Maltese, and doesn't shed his coat, we also make sure his fur is clipped short. He also feels better after a bath or a run under the sprinkler with the kids.
It doesn't take a lot of effort to make sure they are all ok, but it does mean they are as comfortable as possible on these extreme days.