LivePC has an interesting article on how to build one of the most important parts of the water-cooled system - the reservoir. The article goes a little bit farther than just building the reservoir, it shows how to add a window mod. Check it out if you're into water cooling.

Reservoirs, probably the most overlooked part of a water cooling system. You probably think of it just as something to hold the water in your system, but after reading this you will have a change of thought and be able to make a very effective reservoir, with a window kit and all.