The only "kits" that are good are made by Swiftech. Basically, their "kits" are their normal hardware combined into one package.
If by "pre-made", you mean ones that are already setup, it depends on what you want to do. I've heard good things about the H50 if your system is near stock or running stock. If you are going to do any serious overclocking, you would be much better off getting a good high-end air cooling heatsink or a good watercooling system. Cheap watercooling performs worse than "ok" air heatsinks and is far more expensive.