Analytica
Analytica provides consulting and training to the Mathematica community.
HostSRV
A web hosting company dedicated to providing MathScript capabilities to websites.
MathC
MathC provides statistical consulting using Mathematica, visualization of mathematical concepts in the area of teaching Mathematics, and Mathematica-applied college-level mathematics.
MathTensor, Inc.
Developers and distributors of MathTensor, a Mathematica-based package for performing tensor analysis by computer. Formerly MathSolutions, Inc.
Salford Software
Mathematica training and consultancy, The Salford Color Math package, and a list of Mathematica tips.
Scientific Arts
Consulting with Mathematica: Scientific Arts is a consulting and creative services company which provides targeted solutions for a broad range of scientific enterprises.