Migatron
At Migatron, we offer a wide variety of high-quality standard ultrasonic sensors and controllers, as well as design assistance for semi-custom units.
http://www.migatron.com/

Automated Sonix Corporation
Level Sensor, Level Indicator or Liquid Level Sensor, Tank Gauge. Automated Sonix non-contact ultrasonic liquid level monitoring. Display tank level and volume activate alarms, 4-20 ma and RS232C.
http://www.automatedsonix.com/

Hexamite
Ultrasonic positioning systems, ultrasonic ranging systems, ultrasonic transceivers
http://www.hexamite.com/

MS Sedco
Manufacturers of custom motion and presence sensors, specializing in microwave, infrared and ultrasonic automatic door, traffic and pedestrian control sensors and switches.
http://www.mssedco.com

Airmar Technology Corporation
Manufacture marine and industrial sensors using ultrasonic transducer technology. Airducer ultrasonic sensor catalog in pdf format.
http://www.airmar.com/

Reed Electronics AG
REED Electronics AG - Grenzschalter, Schwimmerschalter, Füllstandsüberwachung, Niveauschalter, Magnetic switches, Messsysteme
http://www.reedag.ch/

Ultrasonic Flowmeter Basics
Doppler and transit-time flowmeters are gaining ground in liquid, and in some instances gas, flow measurement applications. Understanding how they work will help guarantee optimum performance.
http://www.sensorsmag.com/articles/1097/flow1097/main.shtml

FT Technologies Ltd
FT Technologies - Manufacturers of rugged ultrasonic anemometers, ISO9001 approved
http://www.fttech.co.uk/

US Ultrasound, Inc.
US Ultrasound designs and manufactures ultrasound transducer, ophthalmic transducer, A-Scan transducer, doppler transducer, piezo transducer, ultrasound array, medical transducer, multi-array transducer, ultrasound probe, ophthalmic ultrasound, linear array transducer, curved linear array transducer
http://www.usultrasoundinc.com

Zevenaar Elektronica & Sensoren
Sensor and electronics design. Ultrasonic and electromagnetic sensors.
http://www.zes.nl