Piezo Systems, Inc.
Off-the-shelf and custom designed piezo actuators, piezo transducers, piezo sensors, ultrasonic devices, and high voltage piezo amplifiers.
http://www.piezo.com

Materials Systems Inc. (USA)
A technology developer and manufacturer of piezoelectric materials, piezoceramics, piezocomposites and piezoelectric transducers for sonar and ultrasonic applications.
http://www.matsysinc.com

Materials Systems Inc. (USA)
A technology developer and manufacturer of piezoelectric materials, piezoceramics, piezocomposites and piezoelectric transducers for sonar and ultrasonic applications.
http://www.matsysinc.com

Ferroperm Piezoceramics (DK)
A manufacturer of piezoelectric ceramics, especially for the fields of vibration sensors, medical diagnostics, flowmeters and underwater acoustics. Page includes list of products and Piezo theory bibliographies.
http://www.ferroperm-piezo.com/

Ilsan Suntek Corp. (Korea)
Manufacturer of ultrasonic cleaning unit, transducers and piezoceramics.
http://www.ilsantek.co.kr/