Corsair H70 Water cool unit. It's very simple to install and self contained, no mess with filling anything, priming pumps, etc. etc. I'm running a QX9770 @ 4 Ghz without a single problem -- Prime95, OCCT, 3DVantage, etc. etc. - rock solid results with 1600Mhz bus. It's about $100 for the H70.
I've done many cooling methods over the years with some of the very earliest Koolance water cooling systems to my own dual pump home brew TEC setup, but the complexity and heat those systems produced (dual power supplies etc. etc.) it just wasn't worth it for a 200-400 Mhz CPU increase over what I run with the H70.
One of the MOST important aspects of the H70 (and why I think it's very superior to any prior method I used) is how the CPU block is attached to the CPU. The H70 distributes the pressure over many many more contact points providing a very solid and even distribution. I think this is why the H70 does so well for such a low cost solution.