It really depends on how much work you're willing to put into making your computer cool
Obviously if you're more concerned with getting it setup and running quickly some sort of pre-made kit is the way to go, but if you like building things - then you should buy each component you think is the best, or more cost effective.
Among premade kits, there is alot o diference, the Koolance or something like that, is the - it doesn't get much easier kinda kit. There are lots of kits, that include radiators, tubing, a pump, a waterblock, and resevoir, that are very similar to things lots of people use here - but with a kit, you don't get to choose every little thing. (unless if some custom kit, which is just like custom anyway...so ...:shrug: )
Dangerden has some kits on their site(175-220 USD), they look pretty good, well rounded and decently cost effective. But as with any WCing in a normal case, if you plan to fit it all in you have to be quite careful when you're choosing all you stuff. (Sometimes not that easy with a kit)
Anyway that's just my .02