Pictured above is my new recirculation chiller. Just did my second brew with it today, and I'm blown away by how fast it cools. It took my wort from 212 F to 112 F in 1 minute! Thereafter, the marginal cooling is about 2-3 degrees per minute. So, took 7.5 gallons of boiling wort down to pitching temperature in about 15 minutes. This thing is amazing.
It works by drawing boiling wort out of the ball valve (pictured left) and recirculating it back up to the top of the boil kettle with the aid of my pump. You can see the silicon tubing and copper return piece in the center of all those lines. The copper return is curved so that returning wort enters beneath the surface of the wort and forms a whirlpool that swirls around the coils of my immersion chiller. This is what enables the 100 degree drop so fast. It's basically super-efficient heat exchange. The other lines are your basic input/output lines for an immersion chiller.
The beauty of adding recirculation to an immersion chiller is that the entire volume of wort can be cooled relatively fast. Other chillers like counterflow and plate chillers also cool very fast, but cool only small amounts of wort at a time. The faster that the entire volume of wort cools, the better will be the cold break, and the more hop flavors and aromas will be preserved by late hop additions during the boil. And at $8 for the silicon and copper tubing, a guilt-free equipment addition I must say.