I'd like to nominate Wigwam socks as bifl, I've been cycling through two pair over the past year and they've out lived three pairs of leather work shoes with no signs of
Merino Wool Thermal Socks, L - 60381 | Klein Tools - For Professionals since 1857
Dissent IQ Fit LoPro Ski Sock - Maximum Warmth + Merino Wool Comfort - DISSENTLABS