Pre-Built water chillers....
 

Check this out. Found one of these at work and it does a great job at keeping the water at a steady rate.

SaltWater Aquarium Chiller

They are aquarium chillers built to keep large water tanks at a specific temperature to simulate an ocean environment. I figure if someone hooked one of these bad boys up to a small tank and then ran another loop for their water cooling rig, it shoud work great!

Let me know what you think.

You only need to plumb the white exchanger tank into your water cooling, no need for any extra tanks. Unless you want to put some fish in the tank.
The bad news. These things are expensive. I stopped looking as soon as I saw $695 for a 1/5 HP unit. And no info on how low the temp can be dropped.

Expensive...yeah. I've been trying to find a deal on ebay for some time now, but no luck.

You might try Googling for some tropical or saltwater fish forums. They might have sell/buy boards just like most of the PC forums.
Here's another interesting chiller, but again $$$. IceProbe Chiller Edit - this won't link properly. Enter and click Chillers on the left side.

You could do what i did... I copied Bender's idea and got a solid state chiller off Ebay. I get -34C temps in the water, and best of all, no compressor. If you want one, search ebay for solid state chiller. The brand is Thermotek.

yo.. im new to the forums so im still reading and gettin alot of info from here... yeh so i dont know how old this thread is but i cant help myself... i love aquariums so let me post some something for yall smarter peeps and see if yall can make anything of it... i dont know much about refrigation stuff.. :D

http://reefcentral.com/forums/showth...ht=diy+chiller

shroomer on EOCF called a big aquarium retailer, and they do not know of any aquarium chiller that will do a good job with the heat we are talking about, they will probably only get the water a couple degrees below ambient, if that. :(