the best i've found are the bridgedale socks. i've only used them in the heaviest weight , for ice, but they have lots of lighter ones too. people i know who sell and use lots of brands tell me these hold up the best and don't lose their bulk. supposedly smart wool socks (which a lot of people seem to love) and thorlos flatten out sooner.
socks that mix wool and synthetics will keep you drier and dry faster than pure wool. but no one's figured out how to make an all synthetic sock that holds its bulk like a wool blend.
i've also had good luck with the patagonia socks, though they've changed the designs many times since i last bought them.
i ususally like a thin liner under my main sock, especially on overnight trips. for this i always use a patagonia capilene sock. they last a long time, don't shrink, don't stink (much) and keep wicking until there's nothing left.