The Analog Devices ADUM4160 isolates and protects a computer from shorts, high voltage, or high currents in a USB device. The isolator chip sits on the D+ and D- data lines between the USB jack and the microcontroller on the USB peripheral. Unfortunately it doesn’t come cheap at more than $5, but it could save your USB port from an errant 180 volt supply when developing that USB Nixie tube Sudoku board.
Many microcontrollers implement USB so that it presents only the D+ and D− lines to external pins. This is desirable in many cases because it minimizes external components and simplifies the design; however, this presents particular challenges when isolation is required. USB lines must automatically switch between actively driving D+/D−, receiving data, and allowing external resistors to set the idle state of the bus. The ADuM4160 provides mechanisms for detecting the direction of data flow and control over the state of the output buffers. Data direction is determined on a packet-by-packet basis.