Personally, for GPUs, I don't really much care, as they're tough to be DOA.
For mobos, I choose Gigabyte, ASUS, MSI, Foxconn, ECS, after their S754, I also choose Leadtek, ASRock seem to have been good with their newer model/
CPU? I go Intel, AMD and VIA.
I kind of change for each system I buy... every time I want a system, I do some research and 'get with the times' and form my own opinion as to what I like the most. At the moment, I'm really liking Inno3D (GPU), AMD (CPU), and Gigabyte (mobo/cpu cooler). I have ALWAYS LOVED Creative, LG, and Logitech also, that's mostly for components.