CPU: None really. AMD in practice. But Intel is currently pretty uninteresting. P4C is still almost nice though. Right now I do not see any good reasons to buy anything other than A-64, for a GP PC. And A-XP for fantastic value and cheap boxes. But that's not bias. Just rationale. I'm hoping for a terrific comeback from Intel in a couple of years.
Memory: None. Cheap thankyou. I don't put too much faith in Crucial & Corsair superiority. I've had excellent results with TwinMOS, Kingston and Mushkin value ranges, but I'd happily buy 'generic'. Some memory don't work right with every MB, so what? Change it, try another stick. I try to buy faster than I will run at though.
Mainboard: Again none. I tend to experiment with 'value'-range mainboards recently. I'm comfortable with single channel, VIA and SIS (I'm comfy with 'em. It's no bias! I go nForce or Intel if I can). $50 is about right for an A-XP MB, IMO.
Never integrated video! I avoid those feature rich MBs, that win reviews and laudels and have lots of features I don't intend to use.
Maybe I like
MSI and
EPoX a little bit better than others, but it's no hard bias. I consider ASUS number one, and for a really cheap box, (Duron) I wouldn't hesitate to try even PCchips (haven't, so far).
Hard Drive: Connor and Quantum 
- Well seriously, (sigh) currently Seagate, Samsung, WD. But I have a lot of IBMs too. The later have worked well sofar. Had tons of problems with early IBM deskstars.
Optical drives: Samsung, LG.
Sound: Creative mainstream board (or possibly on board).
Video: nVidia in practice, I suppose. But not really, I'm an ATI fan as well. But
nothing else. So ok then,
nVidia and
ATI.
PSU: Finally an easy one.
Fortron. Probably some insecurity. I don't know much about PS. I use only FSP.
Case: Steel midi tower. With screws everywhere thankyou. Horisontal mounting for PSU above MB.
Cheap.
Cooler: Zalman and
Arctic Cooling.
Keyboard: I like 'miniature' keyboards. Otherwise I think
Key Tronic is quite OK. I liked the old ones better, but ergoforce is ok. Not a fan of cordless.
Mouse: A4. As high res. as available, on max accs. Never cordless, too heavy.
Game devices: MS Sidewinder Force feedback for everything.
Monitor: Hansol, CTX, Samsung.
Printers: Canon.
OS: Right now -
MS Windows XP pro. I like it a lot, monopoly or not. Haven't liked anything as much since the early Win95, and Amiga OS before that.