GNOME distributors:

Ximian, Inc.
Offer the Ximian GNOME desktop, a full distribution of the latest GNOME packages.

Red Hat, Inc.
Offer GNOME as an integral part of their Red Hat Linux distribution.

SuSE, Inc.
Offer GNOME as part of their SuSE Linux distribution.

TurboLinux, Inc.
Offer GNOME as the default desktop environment on their TurboLinux Workstation distribution.

Software in the Public Interest, Inc.
Offer GNOME as part of their Debian GNU/Linux distribution.

MandrakeSoft, Inc.
Offer GNOME as part of their Linux Mandrake distribution.

LinuxPPC, Inc.
Have GNOME as their primary desktop and have been a long time GNOME supporting company.

Terra Soft Solutions, Inc.
Offer GNOME as part of their Yellow Dog Linux distribution.

HispaFuentes
Offer Ximian GNOME as part of their HispaFuentes Linux 7.0 distribution.

Alphanet Linux
Offer GNOME as the default desktop of their Linux distribution.

Progeny Linux
Progeny is a Debian based Linux distribution which offer GNOME as their default desktop. They also have some distribution specific tools developed with GNOME.

Support providers:

Red Hat, Inc.
Offer support contracts for GNOME in conjunction with their Red Hat Linux distribution.

Linux Care, Inc.
Offer support contracts for Open Source software, including GNOME.

Ximian, Inc.
Offer support and feature development contracts for GNOME.

LogX s.r.l.
Offer support and development contracts for GNOME in Italy.

Essential Information Systems
Offer support and development contracts for GNOME in Spain.

CodeFactory AB
Offer support and development contracts for GNOME in Sweden.

Other:

Eazel, Inc.
Develops Nautilus, the next generation GNOME file manager, and contributes to a number of key GNOME technologies.

Sourcegear
Supports development of AbiWord, a free word processor for GNOME.

Gnumatic
Gnumatic develops and sells commercial support for Gnucash, the personal finance management software.