Resources to use when looking for contractors:
1. http://www.acca.org/
2. Call the MFG of equipment and ask for a list of licensed contractors in your area...i.e.....Carrier....Goodman.....(_insert your favorite color unit here_)
3. The BBB
4. You could ask in here for a local contractor or if anyone can recommend someone I have seen a few threads where someone was able to help someone find a competent contractor in their area.
5.http://www.energystar.gov/index.cfm?c=cac.pr_central_ac
6. ARI website: http://www.ahridirectory.org/ahriDirectory/pages/selectSearch.aspx
(Use this site for research once you have found a contractor that has proposed a system)
Don't limit yourself to the phone book when you have a computer that can be very helpful to you.