Tier 1:
EVGA (very very good high end models and very good warranty, not so good temps on some models)
Asus (good overall quality and aftersales service, sometimes overrated but well deserving most of the time)
Gigabyte (very good build quality, sometimes overpriced and mostly underrated)
MSI (generally above average quality and warranty)
BFG (now defunct)
+ higher end models on several brands like Sapphire (VaporX), Sparkle (Calibre), XFX (Black Edition), Gainward (Golden Sample), Zotac (Amp!) Inno3D (iChill), Why no Palit? Simple, because Palit only offers cards with either reference or castrated PCBs, no beefed-up variants with added extras on phases/vrms/ramsinks/etc..
TIER 2:
Sapphire (heard they were intentionally denying rma on hd5850 extreme batch)
Inno3D (above average mid to high end products, i dont know with others who are claiming to have experienced otherwise, maybe they ought to try overclocking on water an 8800/9800gtx, gtx260/275/280/285 and see for themselves)
Palit (very competitive pricing but fairly average build, local rma process is easy though)
Gainward (same with sister company Palit)
XFX (good build, modest pricing but difficult local warranty)
Zotac (mostly modestly built/priced)
Tier 3:
His, Powercolor, Sparkle, Galaxy, Biostar, Winfast
Tier 4get:
PNY, Leadtek, ECS, Visiontek, Colorful, Point of View, Club3D, Axle, Triplex, Chongkuai-la, Butchikek, EK3x..
Note: Low-end entry-level products barely fit into this picture simple because with cheap models, "YOU GET WHAT YOU PAY FOR". (you cannot expect 1m hours of life and stable 1ghz of clock out of your 2000-peso card, right?)