If you are considering replacing your central air system this year you should consider using a heat pump rather than an air conditioner.
A heat pump will save the same amount a new central air system will, in the cooling season, but will save an additional 25% - 35% of your heating cost. On a call for heat the heat pump will run before the gas furnace and when the heat pump can not handle the load the heat pump will shut off and the gas furnace will run. In this area most heat pumps will handle the entire load of the house to about 30-32 degrees but this will vary from house to house. Below that it will need to supplement with the gas furnace and all control is done with a special thermostat.
This type of Hybrid Heat or Duel Fuel system will prolong the life of your existing gas furnace or with a new more efficient gas furnace lower your heating bills even further.
In the City Water Light & Power service area you will recieve an additonal rebate for using a heat pump. The cost difference between the air conditioner and heat pump can be offset by fuel savings in about one year once you factor in all the rebates and incentives.