See also this list of publishers.
Academic Press
Aces Research, Inc. (Developers of Mathematics
Library Plus)
Addison-Wesley Interactive
Adept Scientific
Advanced Scientific Applications
Inc. (SciMath)
Anton Textbooks, Inc.
Basic Research Institute in the Mathematical
Sciences
Birkhauser AG
Brooks/Cole Publishing
Mathematics Page
Compass Modeling Solutions, Inc.
The Computational Mechanics Company, Inc
(COMCO)
CPLEX Optimization, Inc.
Cross
Educational Software
Elegant Mathematics, Inc.
Elsevier Publishing
GAMS Development Corp. (modeling)
Harmonic Software Inc. (Makers
of O-Matrix)
Key Curriculum Press
Khayyam Publishing Company, Inc.
Learning in Motion
Lemma Inc.
Logix Consulting
Mandalay Scientific Inc. (Data Modeling)
Mathematica (wri.com)
MatheMatrix, Inc.
MathMedia Educational Software,
Inc.
MathPlus
MathPro Press
MathSoft Home Page (Developers of Mathcad)
MathSolutions, Inc.
MathWare (Derive)
MathWorks Home Page (Producers
of MATLAB)
Minitab Inc
Neufeld & Associates
Numerical Algorithms Group Ltd
OPCOM Pty Limited
Pedagoguery Software
Principia Consulting
PWS Mathematics
SGI
Operations Research Initiative
South-Western Educational
Publishing Mathematics
Springer
Springer New York
Steven M. Christensen and Associates,
Inc.
TCI Software Research
Thompson Publishing
Thompson
Publishing Math Catalog Search
TSP International
Visual Numerics
Waterloo Maple Inc.
West Educational
Publishing Mathematics and Statistics
XOX Corporation