I just read about a new very efficient air conditioning system. They call it solar powered since it can run on just a few solar panels. It can use battery power at night.
Here in Arizona this could be very good. I already have a SEER 18.5 Lennox system but this would have been a good choice if it was available back in 2001 when I got my system. Mine also does the heating becuase it's a heat pump and can cool or heat.

Check out solcool.net

Solar-Powered Air Conditioner
by Justin Thomas, Virginia on 03.21.07
Science & Technology (solar)
After 4 years of development, California based company SoCool will launch the Millennia version 4 hybrid solar air conditioner. The air conditioner runs on solar panels, or a wall socket, or batteries. It's designed to cool a large room while substantially lowering electricity costs according to the company. The unit operates at a maximum of 500 watts, which is much than half what typical air conditioning units use. If using batteries, the unit can last up to 24 hours depending on battery size. Priced between $2,600 and $3,000 before installation (approximately $500), the SoCool Millennia includes two-gallon water tank to store cooled water.

Also AMANA has a SERR 24 Heat Pump, If you have a grid tied solar home your air, lights and home all run on solar.