There are a number of options for watercooling. The Koolance system is a good entry point. Alienware uses these for OEM setups. The External system is only $200, the CPU block, $50, and the GPU block, $40. So, for around $290, you are set. It only uses 1/4" (6 mm) ID tubing, however.
If you want to go high end, I would recommend Innovatek or DangerDen. Both are very similar. I use the Innovatek items for my PC. I recently upgraded from the Koolance system. This system is more expensive, and uses 8 mm tubing. They have kits to get you started.
A good place to get the items, and they are very honest and straight forward, is:
I bought all my watercooling items from them. If you have any questions, they are more than happy to help.