A design firm is an organization that designs any of a variety of things, in one or more of the design fields, such as graphic design, web design, architecture, engineering, interior design, or industrial design.
A design studio is similar to a design firm, but may consist of solely an individual designer, whereas a design firm consists of several designers, illustrators, managers etc.
(ELEVEN), LLC - Industrial Design
Continuum (design consultancy) - Industrial Design
Smart Design - Industrial Design
IDEO - Industrial Design
Stefan Sagmeister - Graphic Design