Thermaltake big typhoon is definetly a good overclocking heatsink for a decent price. If you can shell out the money, I would recommend getting a Zalman heatsink with arctic silver thermal grease. Either the Zalman 9500, or the Zalman 9700. Depending on if you want LEDs or not could be the difference between about 5~10 dollars, and if you want the 9700 (which is a bit bigger) or the 9500 could be another 5~10 dollars. Its the best non-liquid cooling money can buy.
well, if your water cooling, you might as well also water cool your graphics card and RAM (if possible) I was reading something about CPU cooling, and it said, that unless your a hardcore render, or Gamer, its useless, your CPU is mainly at <5% usage. I would recommend a Zalman 9700 if you have the case room. Im not an expert with liquid cooling, but I know that air cooling is a heck of a lot cheaper and I would imagine that it requires a lot less maintenance.