I mentioned this last year in my Beef Stock 101 thread.
In restaurant kitchens, we have what we call "Ice Wands". They are large, heavy-duty plastic bottles with an X-shaped cross-section to increase surface area. We fill these with water, freeze them (be sure to leave a little head space at the top so the bottle doesn't break), and use them to cool large batches of hot liquid by placing the bottles directly in the pot.
What I've done is to take a 2-liter pop bottle, remove the label, scrub it clean, and do the fill/freeze procedure. When I make stock, I'll plug the sink, place a cake rack in the bottom, the pan of hot stock, pour ice around the pan, put the frozen 2-liter in, then fill the sink with just enough cold water so that the fluid level in the pan is a little above the fluid level of the sink, so the pan doesn't float. I can chill 2 gallons of boiling-hot stock down to 40 degrees F in 30 minutes this way. The faster it goes through the Danger Zone, the less chance bacteria have to grow, and the stock will have a longer shelf life, although I'm going to freeze the stuff within a few days anyway.
Peace, Love, and Vegetable Rights!
Eat Meat and Save the Plants!