I found cage fans in argos, but then discovered they are a pound cheaper at Pets At Home, so i will link to there.
http://www.petsathome.com/find/keyword- ... t-is-13622
They are very effective with two speed settings, they run on batteries, and can hook on any cage/hutch/run.
I also pinned white shower curtains over half of my runs. The white reflects the heat, while causing a shade over about 3/4 of the run.
I have also started adding ice cubes to the water bowls to keep water cool, and making vegetable ice cubes. Chop up vegetables, pop in an icecube tray, fill with water, and freeze.

I pop a couple in each of the water bottles ( handy they have wide tops) or I chuck a whole big bag in the water bucket and top up all the bottles from there 
