A word of warning about those films--if you have double or triple-paned windows, don't use them. The heat builds up between the panes and causes the seals to break, then you get moisture between the panes of glass. I use the film in our attic windows and the transom over our front door because they are the original 1906 panes of glass. However, the rest of our windows are vinyl double-paned and it can ruin them.
Our best investment was insulated drapes. We have them on most of our windows--they allowed us to turn up the thermostat to 72 degrees from 68 during the winter with no extra expenditure. During the summer, they do cooling duty.
I am seriously missing my central air right now.
It only got down to 82 muggy degrees last night. We have a 10,000BTU portable unit in the dining room which takes care of the entire downstairs, and two 5,000BTU window units upstairs which usually are enough to keep it comfortable, but they were really struggling last night.
Thanks for the explanation about evaporative coolers, Nova. I've always wondered what they are.