I've tried a variety of cooling methods including ice, and trust me, changing that ice everyday will get old real fast.
Most growers probably have a wine celler or basement that stays cool, but I settled for a more expensive option of using a 1/15hp aquarium chiller and a small cpu radiator. It works wonders, the day/night temps are 24/12C, and it can get much colder if I wanted. Without the cooling mechanism, the T5 lights in my tank will make the day/night temps of over 30/24C (night temps is room temp). My tank size is 50 gallons, but a larger tank can probably be used since my chiller isn't even working at max capacity.
I have also seen attempts with peltiers, but they only do something to very small tanks.
Of course, the major con again is definitely cost. It will put you back like $500 canadian for the chiller, the aquarium pump, the tubing (from home depot) and the radiator (from ebay).
chiller and bucket to catch condensation from tubing
Cooled terrarium. Black thing is radiator with cpu fan. Circuitry controls the fan, cooling only happens with the fan is on so you can do some feedback with a temperature sensor to keep the day/night temps at specific levels (I chose 24/12C).
And I can't miss an opportunity to show off my rajah ;D (click for larger sizes)