There are lots of kits out there and many that kick a donkey's ass. If you want to custom your own kit, i suggest (after a few attempts and upgrades) that getting an Eheim pump...1048 or 1250 depending on your desired flow, a Gemini spiral, Swiftech, OCZ, or Silverprop waterblock, and a heatercore from the local autoparts store. Go to the autoparts store and have them look through the books looking for a radiator with the size that you are looking for and pick the cheapest one...should cost $20-30 or so. I personally use the Gemini spiral, an Oldsmobile heatercore, and the 1250 and have not seen my temps (xp1900@2100+ speeds) top over 36º@load on a Abit board. All the blocks I mentioned are have been reviewed on
HardOCP and have gotten great reviews.
The difference between heatercores and those fancy-ass mod-shops' rads is mostly looks.
For straight-up kits:
a review from a reputable source