I live in a desert, sometimes the hottest place in the USA, beating Death Valley. Lots of people here use evaporative coolers, or what we call swamp coolers. If you live in a humid area, then forget it because swamp coolers cool by putting a cool dampness in the air, nothing wet but on a hot dry day a properly sized cooler can cool a 2000 square foot as much as 25 degrees. While this costs money, the 'green' part about them is that they save up to 80% when compare to air conditioners.
The way it would work after installation is you open a door or window and start the cooler. The cooling comes with the pressure built up in your house. The more windows and doors open the less pressure. Too much pressure is a bad thing for your motor, so always leave a window cracked.
With just a motor load, no compressors a lot of money can be saved compared to an A/C. They come in wall mount, window mount, roof mount, portable (on rollers) or just fans with a misting system. The small fans will only cool you if you are sitting right in front of it.
Click on this good ol' Wikipedia link for more information.
Put green landscaping around windows, like bushes or shrubs, to cool the air more when windows are open. On the hot side of the house plant trees to provide shade when the trees grow tall. These might not have immediate affects on your house, but will cool you more when the plants mature.