I can cool my tanks to 78 degrees when my house is 100 degrees, all with fans. I have to replace a gallon a day in each tank, but it's worth it.
The effect of evaporative cooling actually works better with warm air, as the evaporation occurs quicker, which also drops the tank cooler quicker. It's a VERY effective way of cooling. If it's not enough for your tank, get a bigger fan. I have a squirrel cage fan i bought on e_bay for 20 dollars that cools 2 20g longs down to 70 when the room is at 85+, and a tower fan turned horizontal on top of a 20g that cools just as well.
Your other options, such as floating ice packs will help for about 30 minutes maybe up to an hour, and drop the temperature a degree or two before melting and becoming part of the problem.
You could, of course buy a chiller for a few hundred dollars, but a window AC unit costs under 100 dollars usually, and works just as well (for the same cost in electricity).