Manger
Manufacturer and developer of a transducer controls the complete frequency range from 80 Hz to 35 kHz on its surface. Makes also loudspeakers and subwoofer. Germany.
http://www.manger-msw.com/

Sensor Technology Limited
Sensor Technology Ltd. offers piezoelectric materials, acoustic transducers, hydrophones, actuators, instrumentation and systems for applications such as marine navigation, geophysical surveys, underwater explorations, broadband acoustic transmission and laboratory research.
http://sensortech.ca/

Frequency Selection Database
Resource for USA frequency coordination and spectrum research.
http://www.spectrumwatch.com

Luff Research Inc.
Manufacture high performance RF frequency synthesizers and phase-locked frequency sources.
http://www.luffresearch.com/

ZZAP Elektronik d.o.o.
frequency converter, power supply, radio frequency reader, frekvencijski pretvaraci, izvori za napajanje, ups, radio frekvencijski citac, web design, web dizajn, electronic components, elektronicke komponente, konzalting, consulting, internet
http://www.zzap-elektronik.com

Liteline Electronics
Lightline Electronics, products for the motion picture industry. Maker of the CineSpeedMeter2 and other precision frequency measurement products.
http://www.lightlineelectronics.com

Liteline Electronics
Lightline Electronics, products for the motion picture industry. Maker of the CineSpeedMeter2 and other precision frequency measurement products.
http://www.lightlineelectronics.com

Elmika Microwave Technologies
Sweep oscilators, scalar and vector analizers, frequency converters, attenuators, frequency meters and waveguide components.
http://www.elmika.com/

References on Zipf's Law
An academic bibliography on this relation between a word's frequency in a text and its place in a ranking of words by frequency. Includes some online texts.
http://www.nslij-genetics.org/wli/zipf/index.html

Alexej Jerschow's Interactive NMR Frequency Map
Very useful resource. You enter the proton Frequency, the range you want to see, and the spin. The table prints out a very handy chart of the receptivety of the different nuclei.
http://www.nyu.edu/cgi-bin/cgiwrap/aj39/NMRmap.cgi