Whenever I need a seriously fast box I call the guys at Maingear and have them build one. Tuning a machine, matching all the components and so on is a area I no longer spend the time to keep up with - those boys are on it like hot-rodders are all over engine specs.

Other than that? I recommend Intel CPU's and nVidia graphics cards. Neither have ever let me down in production - which is more than I can say for ATI :)