I've been using the same basic Ice chest fog chiller from HERE that I see a lot of others using. I was going to build another one this year, but due to time restrictions I decided to just modify this design and it really seemed to work out pretty well for me. I call it the "muffler mod" since the finished product looks very similar to a car's muffler. Basically after looking at the original design I had 2 thoughts. 1) Since there is almost no restriction the fog pretty much rushes out the outlet. 2) With the single pipe design you have a very limited contact area for the fog/ice and it seemed like a ton of wasted space and ice.
Here was what I did in a nutshell.
1) I added a baffle to the original 4 inch mesh pipe to slow the flow of fog through the chiller. Nothing fancy. 2 plastic 4 inch test caps for PVc pipe from Home Depot. Screwed them together and then attached them to the pipe using screws and a couple of washers.
2) I created a second cylinder (about 8 inches round) out of the same hardware mesh. I also created mesh end caps. Once that was done I cut a hole in each end big enough to slide the original pipe through the center and wire the larger cylinder in place. I figure this effectively doubled the chamber size.