I also use one of those window fans. It has two fans in it and you can set each individually to blow in either direction. Due to our (Calgary) low humidity, the temperature really drops at night, pretty much as soon as the sun goes down. The fans have little value during the day.
If you spend a few extra bucks you can get a fan with a thermostat that will shut the fans off if it gets too cold.
The downside with the fans is that they are very location specific. It only impacts the single room it is in.
Here is a pimped out version:
http://www.amazon.com/Bionaire-BW230.../dp/B000065DKJ