The USB-COM-PLUS family of communication modules from Future Technology Devices provides dual port capability for the RS422 differential and RS485 multipoint differential interfaces. All multi-port modules feature a USB 2.0 Hi-Speed (480 Mb/s) interface, and feature a 5 V output that can provide up to 250 mA. The operating temperature range is from -40 degrees C to +85 degrees C. From $19.
Future Technology Devices
503-547-0988, www.ftdichip.com