Below is my list of "don't buy". I've included reasons for each one because the fact that I wouldn't buy from them does not automatically make the brand universally poor.
OCZ - Quality is all over the place. Really have to dig into the reviews to see where each component stands. Some decent, some not so much, nothing really "great".
Thermaltake - Same deal as OCZ. Not inherently bad, just too hit and miss for my liking.
HP - Their enterprise offerings could withstand a nuclear blast. Their consumer offerings can't even withstand minor changes in air pressure.
Toshiba - Decent products for the price, but they generally don't make an impression on me.
Acer - Same deal as HP, but worse.
Biostar - Cheap chinese garbage
EVGA - EVGA Graphics cards are generally pretty good, but not always outstanding. Everything else is a total toss up from a quality standpoint and generally overpriced. There's almost always something better offered by someone else for the same price. Their warranties do kick ass though.
ASRock - ASRock is a spinoff from Asus meant to compete with budget manufacturers. They do tend to be on the upper end of budget in terms of quality. There's nothing wrong with ASRock at all, I'm just not a budget shopper.
Below is my list of "do buy".
Asus - They have the best motherboards, no contest. Their other offerings are generally pretty good too. Seriously, when I go shopping for a motherboard I don't even look at other vendors anymore.
MSI - My personal experience with MSI is limited but they've been making some serious inroads in the enthusiast markets recently and have been bringing some serious competition to markets historically dominated by Asus, EVGA, and Gigabyte.
Corsair - Does this really need any explanation? They have some of the most recommended memory modules and power supplies around, the best case fans, and now the best cases.
Mushkin - Corsair quality memory for half the price.
Kingston - Some of the highest quality memory available to consumers. Manufactures ECC RDIMMs as well.
Samsung - Crowd favorite for non-volatile memory. The Samsung 800 series SSDs kick ass.
Sony - Comparable to Samsung. Their laptops are rather nice for the price.
Seasonic - They offer the most reliable power supplies available and manufacture PSUs for Corsair and XFX.
Enermax - a PSU manufacturer in line with Seasonic. A solid substitute where a Seasonic PSU is not an option.
XFX - SeaSonic PSUs + good quality graphics cards with great, transferable warranties.
Antec - High quality, affordable cases. The build is generally conservative (a departure from some of the silly designs out there) and of higher quality than most competitors excluding the premium ones from Corsair.
Swiftech - One of the few manufacturers to actually offer an entire suite of watercooling products
Logitech - My keyboard has a monitor on it, your argument is invalid. Also, my mouse is comfortable and actually looks like a mouse.
Dell - Their bottom end products are mediocre at best but their enthusiast, business, and enterprise offerings are generally of very good quality.
Lenovo - Great business laptops for a very good price.