Overview of ACEEE:
The American Council for an Energy-Efficient Economy is a nonprofit, 501(c)(3) organization dedicated to advancing energy efficiency as a means of promoting both economic prosperity and environmental protection. ACEEE fulfills its mission by

-Conducting in-depth technical and policy assessments
-Advising policymakers and program managers
-Working collaboratively with businesses, public interest groups, and other organizations
-Organizing conferences and workshops
-Publishing books, conference proceedings, and reports
-Educating consumers and businesses

ACEEE recommends EER of at least 11.6

This ensures the unit is efficient throughout the year and when it is needed most (on the hottest days). If you live in a hot-dry climate, ACEEE recommends a high SEER (15) but a high EER is less important: 11.5 or 11.6 is adequate. Better yet, consider an evaporative cooler instead.

How much money can I expect to save?
That depends on the price of electricity. You can compare the cost of running a new air conditioner to the cost of running your existing unit using the ENERGY STAR savings calculator. Just enter the price you pay for fuel or electricity from your utility bill. The ENERGY STAR savings calculators are downloadable Excel files; click to download the calculator you would like to use: central air conditioner or heat pump.