I have no A/C. With a 10" fan blowing directly on the water, a bubble wall in the back (yes, I know it looks tacky, but it's for the tank's health) and lights not coming on until the heat of the day is past, I can keep the tank 10 degrees cooler than ambient temperature through evaporative cooling. With a saltwater tank you'd want to rig up an auto-topoff to go with that so you don't have other side effects.
The bubble wall has a secondary effect of very quick gas exchange. Even though I'm not running a fast-growth tank, my plants sometimes pearl due to the super-saturation of gasses in the water from my bubble wall.
I currently have a Neptune Systems AquaController Jr on order to further control situation. I don't really trust my heater thermostat, and I'd like the fan and bubble curtian to automatically cycle on/off as needed.