5. Aqua Sock
Designed by Geoff Hollister, the Aqua Sock was about as simple as a shoe could get - a slip-on sock with a thin rubber outsole. That was it. (1991's Aqua Sock Too and Aqua Sock Classic provided a little more structure.) They were meant for water sports (no, not that kind, perv) but also were an early vanguard of the minimalist movement.