Some people freeze water in 2L bottles and put them in a water bath, which also has the fermentation vessel (carboy?) in it. The ice and water helps distribute the cold, but knowing how many to put in there is key.
I believe they usually have enough on hand to rotate into and out of the water bath, so that there aren't extended periods of time with no ice. Sounds like a lot of work, but might help prevent off-flavors during the critial early stages of fermentation.