-AMD has been trending the wrong way for a long time, but I've loved their CPUs and (after acquiring ATI) GPUs going back to the Thunderbird & Athlon XP, and Radeon VE. I still run an AMD 6-core, 2x GPU setup and have been happy for a long time.
-Motherboards: ASUS. I've had good experiences with Gigabyte too, however. I also miss Abit.
-Video Cards: Sapphire, but I also really like EVGA (great customer service), and I miss BFG Tech (awesome warranty & support)
-PSUs: Antec. No question in my mind.
-Fans/Cooling: Also Antec when I can get them. Really long-lasting, and good performance.
-Memory: Holy smokes it's G.Skill these days. Samsung has top-end quality, Corsair has great customer support, but I have been very happy with G.Skill for several builds (good mix of quality, price, warranty, and great support)
-Sound: I've always liked Creative, but steer towards Realtek chips now (like many), and have been happy for what seems like forever with my aged Auzentech 5.1 X-plosion card.
-HDD/SSD: I mix Seagate & Western Digital for HDDs, both have been pretty solid for me. Oddly, I've only owned a single SSD, and it's an OCZ Vertex. Up-to-date firmware has been very kind to me. Fast with no problems.
-Optical Drives: It's LG, easy.
-Input: SteelSeries (or Ideazon, going back a little). Microsoft does well here, too (mice, controllers).
-Peripherals: ASUS. Wireless NICs, Bluetooth adapters, etc.
-Networking: ASUS. I like DLink too. Netgear and Linksys have not been very good to me. Won't go back.
-Monitors: ASUS. I have a thing for Viewsonic too, but they haven't done as well with LCD/LED panels as they used to with CRTs, they were the best.