Below are some useful measurement and analysis tools–with relevant descriptions–that can be found on the web. 

Acoustics Engineering (Sabin and Dirac): 
Developers of Sabin andt Dirac acoustical software

Brüel & Kjær: 
Measurement microphones, sound level meters, analyzers etc.

Davis Instruments: 
Test Instruments for Industrial Applications

DRA Laboratories: 
Developers of MLSSA acoustical measurement system

Gold Line: 
Manufacturer of numerous audio / acoustical measurement devices plus owner of the TEF line of acoustical analyzers

Integral Acoustics: 
Manufacturers of some neat little software products for various acoustical and electroacoustical applications – some of them freeware

Loudspeaker Acoustical Room Analyzer (LARA)

Larson Davis Inc.: 
Manufacturers of noise dosimeters, sound level meters etc.

Liberty Instruments Home Page: 
Developers of the IMP, IMP/M and Liberty Audiosuite audio analysis systems for loudspeaker and electronics designers

Manufacturers of the LMS Loudspeaker Measurement System software

Ptolemy Services: 
Developers of Jade environmental noise monitoring and dataloging software

Pure Bits: 
Manufacturers of “Sample Champion Version 2.0” – very nice acoustical analysis software with surprising functionality. They also offer some really neat downloadable wallpapers (free)

RPG Diffusor Systems, Inc.: 
Great source for acoustics background information. Developers of RPG Room Optimizer software

SIA Software Company, Inc.: 
Developers of SIA Smaart (formerly known as JBL Smaart) acoustical measurement and analysis system

Sound Technology – Spectra pcSeries Softest: 
PC-based test, signal processing, data acquisition and instrumentation software

Manufacturer of the Audio Toolbox – nice low-budget measurement tool

Test and Measurement: 
Virtual community for the test and measurement industry

The Speaker Building Page: 
Interesting acoustical shareware and freeware programs

Sound Devices: 
Manufacturer of a portable USB audio interface with built-in 24 bit A/D converter and +48V phantom power – powered by the USB port! Perfect companion for many audio / acoustical measurement software packages

Windows-based MLS measurement software