another tip or two for saving a bit o' cash on your electric bill...
either use window blinds or curtains and keep them closed for the hottest parts of the day
using ceiling fans in most rooms at the least makes it feel cooler, so you can get by with a couple less degrees lower temps on the thermostat
make sure your outside ac coils are CLEAN. if they can't flow the air it will take longer to cool down
change your air filter , this will also increase air flow helping your ac unit to do it's job more effectively.
lastly, on your blower/heater unit inside, their is a thing called an a- coil
so named because it is shaped like and "a". this is just like the outer coils.
if kept clean the air will flow better and your ac will run at top effeciency.
the last one might be best to leave to a pro, but the others are easily done yourself.
if you can afford more insulation in your attic adding another 6-8 inches will make a world of difference also