FYI, the fans DVS talked about are great for cooling lighting. I have two of them for my lighting, but the water was still running around 83-84. I really wanted it at 80. Chillers are a great solution. Unfortunatley they're expensive, and take up space. If you have money and space go for it. Otherwise use a small house fan. I have it on top of my sump facing down. On low it has dropped the temp to 80 perfect. The only downside to fans is evaporation. I don't mind doing manual top-off every other day. It also helps me dose Kalk, but I think I'll get sick of it sooner or later. Your tank, your decision.
One more thing. A guy at my lfs said I could have the fan blow across the front of the tank to cool it down without as much evaporation, but my wife isn't really up for that, so I haven't tried it.
