Thorlo S1TOU - make sure they say 'Ultrathin'! These have seriously good wicking, (good enough to stay dry when winter cycling) The labeled sock sizes are kind of crazy though, make sure you look at the corresponding shoe size. Do *not* just grab a 'medium' or 'large' sock!
Wigwam Ultimax Snow Whisper Pro - these are *not* anywhere nearly as good at wicking as the Thorlos above, but they are a bit more affordable. And the elastane material makes getting into tight boots considerably easier. And they last forever - this model used to be called just plain Wigwam Ultimax about 6-7-8 years ago, and I still have a stash of perfectly good neon green ones from then.
Ever so slightly thicker than the two above:
Smartwool PhD Ski Ultralight - good wicking, not as warm as the Thorlos.
Darn Tough Mens Merino Ultralight - only just got some of these
Last but not least, do you have a really tight fitting boot? As in race fit?
If you do not, and if you fly to skiing a lot, may I recommend the CEP Progressive+ Thermo socks. Yes, they're $50. Yes, they're slightly thicker than the Smartwool and Darn Tough. Yes, you have to size them based on calf size. But you can wear them on the plane and ski in them. And, when you're just starting to ski at altitude, they can help with after-first-day foot swelling. So your boots are easier to get on on the second day.