Because of Linux's 24/7 reliability, scalability, performance, and configurability, it can make a powerful IT resource for any company. When you consider Linux's low cost (zero per-user license fees are just one exmple) Linux systems are even more attractive.
A partial list of Linux business resources is maintained at http://www.linux.org/business/index.html, and is a good place to look for more information.
A recent example in the press is Total Travel Management, in Troy, Michigan. You can read about their conversion to Linux here.
The Gartner Group recently released a short article that does a good job of making a business case for Linux.