FYI and thanks to RWebb for the tip, I found this website. Lists tax credit, rebate, and other incentive programs at federal, state, local, and utility level for efficient appliances, building efficiency improvement, and renewable energy systems.
http://www.dsireusa.org/
Looks like a sufficiently efficient split-system A/C would qualify for a 30% federal tax credit and some (need to calculate) state tax credit. Federal credit applies to installation cost as well. Have to do it before 12/31/10.