Another part of my major equipment-building binge (after the fermentation cabinet and MLT), I built a counterflow wort chiller.  In previous batches I had been rather annoyed with waiting for the wort to cool - once I stupidly put it straight into the fermenting bucket and let it cool (which took something like 8 hours), and then I tried cooling it in the brew kettle in a sink full of ice water - an improvement, but still slow.   In the interest of speeding up my brewing process, and reducing the chance of contamination of the wort, I decided it was time for something better.

I pretty much based this on the design at http://www.thegatesofdawn.ca/wordpress/homebrewing/wort_chiller/ 

Materials
All parts from Home Depot and Wal-Mart - Prices are approximate

20 feet of 3/8" soft copper tubing - $25 (HD)
1/2" copper tee sweat fitting (qty: 2) - $3 (HD)
1/2" copper end caps (qty: 2) - $1.50 (HD)
2 foot piece of 1/2" rigid copper tubing - $4.50 (HD)
Hose clamps (qty: 4) - $2.50 (HD)
Zip ties (qty: a bunch) - $1.50 (HD)
50 foot medium duty garden hose - $10 (Wal-Mart)

Total: about $48

The little things are costly in small quantities - the small parts (everything but the hose and 3/8" tubing) were about $13 for hardly a handful of stuff.  If you have some of it on hand already, you can knock the cost to build down quite a bit.

Tools

Pipe cutter (or at least a hacksaw)
Propane torch
Plumbing solder (preferably lead-free, but it won't be touching your wort so that's not critical)
Plumbing flux
Sandpaper

The fittings are built just like Ron's design, but without the soldered hose fitting.  I chose to simply clamp short pieces from the end of each hose to the fitting, so I don't need a separate hose too hook up the chiller.

I also did not bother soldering the spiral of wire on my copper tubing.  It does seem to me that it would improve efficiency a bit, but I didn't have the wire on hand when I built it, so I decided to go without it.

Feeding the tubing through the hose was much easier than I expected.  The hose was more of a slick plastic on the inside, not a more 'grippy' rubber as some hoses might be, so the tubing slid through quite easily.  I got all 20 feet through without having to use any form of lubricant, and without having to struggle with it - it just went through.  I cut the hose after I had run the tubing through it, several inches longer than I expected it needed to be.  

Next, I did the coiling.  I used a plastic spring water carboy to wrap it.  Because of the shape of the carboy, it took a bit of work to get it off, but not bad. 

Next, I cut the hose to length on each end, leaving enough room for the fittings and for a couple inches of copper tubing to stick out.  I slid the hose back enough on each end that it wasn't touching the fitting during soldering, to try and minimize melting and burning it.  I soldered both fittings in place, slid the hose back onto them, attached the two short feed hoses to the remaining part of the tee fittings, and tightened up all the hose clamps.

Because the purpose of the CFC is to cool wort from just below boiling down to pitching temps, I needed a way to siphon boiling-hot wort.  Normally for siphoning I use an autosiphon and regular vinyl tubing, but neither is particularly suitable for temperatures near 212F.  I ended up making a new racking cane out of about 18" of 3/8" copper tubing, to which I soldered a 1/2" copper end cap to hold the inlet off the bottom of the brew pot, just like the black plastic tips you see on regular siphons.

I used a piece of reinforced PVC hose to go from the copper racking cane to the inlet of the CFC, which I was told is safe for use with the hot wort.

Testing

I did a test run of the chiller by boiling a big pot of water and hooking the CFC up in the sink.  I found I was able to get the outgoing wort down to ale pitching temps very easily, especially with the faucet fully on.  I didn't record detailed temperature readings, because the test was somewhat unrealistic - it's currently only the end of May, and our tap water is extremely cold - in the mid to low 60's - and during the summer, when I will need the CFC the most, the tap water will most likely be quite a bit warmer.  However, it was cooling to pretty close to the tap water temperature, within a few degrees, so I was quite impressed.