I used a single cpu Abit board in my previous system. Good board overall, but I wouldn't say my system was exceptionally stable.
For my recent project I used a Supermicro 370DLE. Onboard ethernet and it requires registered ecc ram, but this baby is rock solid! To test I ran the linux kernel build process for 13+ hours in a loop -- not a single issue and the whole system stayed very cool inside my Antec sx1030B case.