hmmmm well you should aways choose custom parts. i'll start you off. would help if we kinew which cpu and gpu you are using.
Swiftech Storm 4/5 CPU Block
Maze 4 GPU Block
A twin or triple 120mm radiator
now the pump is a tricky one. some say you should get a specialised "watercooling" pump. if you go that way then one from Swiftech would be best. all the pros i know use Eheim aquarium pumps though. the difference is the aquarium pumps are AC and the specialised ones DC.