I recently built a wort chiller for brewing beer. There are two kinds of common wort chillers: one is an immersion cooler, where you have a coil of copper tubing that you sink into the wort after its finished, and run cold water through. The other, better way to do it, is by building something called a jockey box. A jockey box works by extracting the wort from the pot it was boiled in, and running it through a copper coil that sits in an ice bath in a generic cooler. The wort comes out on the other end of the box nice and cold. This is much like how air conditioning works.
Here are some pictures:
