Asus is my pick, next would be MSI and then Abit.
ECS, FIC, DFI, and Gigabyte, I try to stay away from these.
I can't comment on these though AOpen, and Tyan.
I get put off by Soyo because the price is cheap, but apparently they reliable, my friend has one with a Duron 850 running in one, no problems at all.