The boot socks I wear are both Free People. Unfortunatly, the cream, ruffly ones sold out a few months ago. But here are a few good options.
I think the key colors for boot socks are cream, navy, maroon, & black.
Make sure and get some that are cable knit or have buttons/lace/etc. Please, do not wear your gym socks... or in my case, my dad's gym socks.