Just my 2 bits on this:
All of the current are wonderful suggestions (fans, digital thermostats, et cetera). I use all of them. However, I also went a step farther (those of you who know me, this is no surprise)....
Our house was built in 1975. It has single paned windows, non-zoned AC, and leaks around the doors and windows so large you can see LIGHT and feel a breeze during the winter.
Our eletric bills WERE around $280 - $300 (2450 sq ft house w/ pool), and I've been doing some calculated efforts over the past 6 months to see if I could adjust that.
First off, go to Home Depot/ Lowes/ Local Home Improvement store and get some of that expaninding foamy stuff that you spray in cracks and wall joints. Go CRAZY with the stuff. Spray it around exterior wall outlets, the seam where your fireplace meets the wall, everywhere. It made a $25 / month difference in my bill during the winter (Gas only for heat) so imagine how much better it can be during the summer.
Second, seal all the doors / windows. If you have windows that you will not be opening, you can get a "Second Window" which just goes into the window opening (mounting on the inside or outside). They don't open, but they add an air-space which helps to insulate.
Thirdly, check your insulation levels. In our house, we had NONE (I don't mean just a little bit, but literally NOTHING). We had R35 put down in the attic, and it made a 25 degree difference upstairs. We are getting ready to have insulation "blown" into the outter walls of the house.
All of these things (insulation and sealing) should run you around $3K. If you save $25 - 30 a month, it takes about 10 years to recover (just keep that in mind). I'll let you know when it gets to be August this year how much we saved over last year, and then everyone can make up their own mind.
The final thing to consider is your Power Company. I shopped rates, and recently change my Power Company. Since I WORK for a power company, I cannot and will not say who I used to use, nor who I am now subscribing to. However, by doing this I have seen a $30 drop in my monthly bill. Couple this with the above improvements, and my bills now run sub $200 ($100 less per month). That makes a big difference.