The easiest entry to water cooling I know of is the Zalman Reserator v1.0+. These are very simple, totally silent and can be had new for £130 or they come up on MM regularly for about half that. The downside is that you have a 3' black missile in the corner of your room and the actual cooling performance is only as good as the best air coolers.
After that, you get into the Alphacool CoolAnswer III type system where you buy a completely built single unit that hangs off a 120mm fan port. The Laing DDC version is every bit as good as a component system and, for £150, you would expect it to be. The downside with those is that the mounting requires plenty of space around the 120mm fan aperture and you really need to check this out to make sure the case will definitely fit. The Coolermaster Stacker definitely fits, because that's the case they use in the brochure photographs
Moving on from that you get the pre-built systems like the Koolance PC3-725 or the Alphacool Ready2Go. These take high quality cases and pre-mod them for you so everything is all neatly built-in and ready to run. They even come pre-filled.
You can also buy the cases with just the radiators so you can choose the tubing, pumps, blocks etc.
Then you get the purist stuff. Anything by Swiftech or Danger-Den is good. Don't be fooled by the Swiftech kits. They have just taken their own excellent components and put them in a box together. As already mentioned, you'd have to be extremely picky not to be happy with a Swiftech kit.
I've got a Koolance PC3-725 system which I would not honestly recommend as, although it is excellent, it is quite noisy in the performance mode. I also have a custom made Lian-Li V600 passive system that uses Alphacool Cape Cora radiators, EK blocks and a Laing pump, but that was VERY expensive.
If you only want to spend your money once then I would recommend you to buy the Alphacool Pre-modded Lian Li G70 case with the triple radiator built into the roof. That is £230, but it is very nicely done and it will handle any water-cooling task you could ever imagine. I would then buy a Laing DDC Pump (with the micro-reservoir) and your choice or Swiftech, Danger Den or EK blocks.
That lot is going to cost you about another £170, so not far off £400 all in. If you accept that the Lian Li would have cost £160 to start with then it's still £240, but it's incredibly neat and as powerful a cooling system as you could ask for.
Doubtless my recommendations will have their critics, but it's a very small difference between what I am suggesting and other people's preferences. Once you have decided that you want proper water cooling, it's hard to really screw it up.
