You can't go wrong with either Asus or EVGA. Those two are definitely the top-tier manufacturers with proven quality in both hardware and customer service. I've also always had good luck with MSI's video cards and motherboards, and a lot of other people would agree.
Never actually purchased a Gigabyte, but I've heard horrible things about their customer service on numerous occasions, and would probably look elsewhere, though the hardware is probably alright. Galaxy makes fairly inexpensive cards - except for the HOF series - and I can't really comment on build quality; they seem to be average at best. Sapphire has been around for a long time, but again I've never owned one, and would probably buy an Asus or EVGA at the same price point regardless. I used to like HIS cards back when they didn't look like the designers went ham on the cards' cooling shrouds... I'm sure it's still the same hardware, but it seems there are better options these days.
I probably wouldn't buy a PowerColor card... maybe I'm wrong, but I've always seen them as the 'budget' brand that stands as a last resort. I apologize to you owners out there that I just offended.
Ultimately, there are a lot of 'decent' companies out there (HIS, Gigabyte, XFX, Sapphire...), but the problem is that when the same thing from a company that's been proven as reliable (EVGA, Asus, MSI) is available at the same price point, there's no reason not to take the latter. At least, that's just my opinion.