4-Port USB to RS-232 w/ Optical-isolation, Surge Protection, Metal Case
USB to RS485 Isolated adapter / converter
You can build your own isolated USB Cable - EngineerZone Spotlight - EZ Blogs - EngineerZone
Amazon.com: COMMFRONT Industrial USB Isolator, USB 2.0 5000Vrms Isolation (per UL 1577), Low and Full Speed Data Rate: 1.5Mbps and 12Mbps, Plug-n-Play, No Drivers Required : Electronics
USB-ISOLATOR - Single Port USB Isolator - ACCES I/O Products
Adafruit USB Isolator - 100mA Isolated Low/Full Speed USB : ID 2107 : $34.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Optically Isolated 7-Port USB Hub - Sealevel
Black Box USB TO RS232 OPTO-ISOLATED CONVERTER (SP385A-R3)
Optically Isolated 7-Port USB Hub - Sealevel
Optically Isolated 7-Port USB Hub with SeaLATCH USB Ports - Sealevel
AZSMZ opto isolated USB MIDI Converter from AZSMZ on Tindie