Well, for pure value and money's worth, you can't beat Cathar's storm/G4 waterblocks (I think they're 2 seperate waterblocks, one more expensive than the other).
They beat everything that's out there right now, and will last you a long long time.
Radiator is another big aspect of the system. For ease of use and install, go with the Thermochill 120.x series. They'll serve you well as they have served me, just make sure you close that bleed valve tight if you don't intend on using it (which is risky buisiness, I've had a stea, of water shoot out onto my desk from it).
Pumps are very important as well. A pump makes the difference between a decent system and one that will blow the doors off anything from dangerden and the like, so choose well. I'd personally go with something like the AquaXtreme pump from CoolTechnica, although others might suggest something a little more robust like the Iwaki pumps.
As far as the rest of it goes, Tygon is good if you can afford it, and don't forget fluids!
You want distilled water with some sort of additive (although if you can possibly do it, pure distilled water is just about unbeatable when it comes to performance, as antifreeze thickens the water)