Companies have been able to harness the power of Debian's participatory model by:
Creating derivative distributions (like in Brazil)
Paying volunteers to work full-time
Support, documentation, etc.
Because Debian's model is participatory, it is resistant to the type of "cooptation" that can be a problem in less participatory systems.
Companies who have sold or contributed to Debian include: HP, SGI, Lindows, Stormix, Progeny, Credativ, and many others.