As reefreak29 said, there are a number of cheap to moderately priced fan units that can be installed on the sides of sumps or aquariums to fan over the water. However, if it is really hot then this may not do too much.
I wouldn't recommend cold water changes since my friend tried that and the shock killed some of his fish. However, if you do cool water changes carefully or gradually it may work for a while. Also, unless the ice cubes are made of salt water, the number needed may dilute the water.
There are plans on some sites for DIY chillers made from tubing and mini refrigerators but as I said, it really depends on how hot it gets where you live. It gets 95 degrees inside my house during the summer so I HAVE to have a chiller. If it doesn't get that hot where you are, fans, ventilation, and perhaps slowly adding cold water may cool your aquarium. Hope this helps,
Mike15.