I bought a big green tub from Meijer (like Wal-Mart). I fill it half way with water, put the fermenter in there, and wrap it in a towel that drapes into the water (for wicking / evaporation purposes). If I want to drop the temperature more, I can cycle frozen water bottles in and out. I'm able to easily keep my beer in the low 60s using this process.
If you don't want to do that, I suggest you look into brewing Belgians.