I use my Yooper Lagerator. It's an Icecube cooler, with a new lid made of styrofoam so that the airlock peeks through. (See my gallery for pictures). I could have used the old lid, but it wasn't insulated, and I can just put on the regular lid if I want to use it as a cooler.
I put the carboy in, then put water in it. Then, I add a couple of frozen water bottles and keep it in the basement. Changing water bottles every three days in the winter keeps it at 34 degrees as long as I want. I can lager in this for 6 weeks or more. In the summer, I can change the water bottles daily and keep it in the low 40s.
Broken Leg Brewery
Giving beer a leg to stand on since 2006