Made with 75% Ultra-wicking Micro Denier Acrylic, 15% Nylon, and 10% Spandex, Bike-Pure socks are produced by The Sock Guy, and I'm wearing Size L/XL. They're also available in S/M.
Bike Pure has an online-store, here, but you can get stuff like the socks from your local IBD, if they'll stock it. I know that I get mine from BikeTek in Pittsburgh.
Now get out there and ride!