Designer Vivek Nagrani produces a limited edition of Mondrian- and pop art-inspired socks each season. Which has a way of sending his loyal customers—who've grown addicted to the Italian and French cotton that never loses its shape—into a tizzy. One man offered $100 to replace a single sock. So Nagrani, whose studio is in New York, rewarded such loyalty with the 21 Club, for men who buy 21 pairs in an 18-month span. Among other perks—such as being alerted to new styles—members have voting rights on which socks from a past collection to bring back. From $30 to $45; vknagrani.com.