Can anyone suggest a good unit that hopefully qualifies for the rebates and tax incentives? I need to replace a 24 year old unit but I only want energy efficient.

There are many units available that will qualify for the second round/extended year of tax credits. Your best bet is to contact local HVAC company's since you will be buying the equipment from them. All manufactures offer equipment that will comply with the tax incentives but the company you want to find is one that does a great job of installing the equipment to start with. You can take the best equipment and turn it to junk with a bad installer.

The higher you go in efficiency the better the installer/startup person needs to be. The 15 SEER and up A/C units are critical charge machines and the R-410A refrigerant machines need a bit more care on the install end also.

Check around with your friends or the BBB for a list of good company's then get 3 bids on the job. Always compare apples to apples if you know what I mean. If you wish post the results of the bids here and we will all pitch in to give you our thoughts on the different brands and bid prices.