Increase air circulation. Operable windows, especially those that are properly shaded, can keep the interior nice and cool. Windows such as these transom types can be left open at night to let in the cooler evening air.
I like the idea of 'hopper' windows (the ones at the top) for the window at the top of the stairs - would be a good way to bring in air upstairs. It would have to be covered with a fly screen though.