Benchtest.Com
Hobby site dealing with CPU watercooling. Several examples of home built watercooling equipment, as well as information on fabricating waterblocks, radiators and resevoirs.

Swiftech
Company which fabricates and sells watercooling equipment. Also provides pre-built watercooled systems to the end user.

BE Cooling
Manufacturer of the Aquastealth watercooling system for PCs. Provides product information, watercooling basics and technical support

DangerDen
Manufacturer of watercooling kits and waterblocks, radiators and other watercooling equipment.

Water Cooling
Devoted to water cooling a computer.

Tekheads UK
Selling watercooling, overclocking bits, and case modding parts throughout the UK and Europe.

Cooltechnica.com
Selling watercooling products and fully customizable AquaXtreme Water-Cooling Kits.

Bobnifty's World HQ
Tutorials on CPU watercooling, hardware modifications and case modifications, like window cutting and painting.

Athlon Watercooling Adventures
Details the installation and testing of a water cooling apparatus for a AMD Athlon processor.

Extrememhz.com
PC cooling and tech source specializing in water cooling.

ICEe Computers
Water cooling and case modding information.

Watercooling 101
Forums, reviews, guides on watercooling.

Overclockers.com - Watercooling Section
Several reviews and user tips on water-based cooling systems for PCs.

ThermoChill
ThermoChill is a manufacturer of PC watercooling equipment and case modification hardware.

Horse of Iron, Inc.
Manufacturer of cases, fans and watercooling hardware. Pictures on web site show detailed information of products.