GainIndustrySupport
It is important to contact companies who sell computers or produce hardware to keep the pressure on to support Linux. Just find their contact info and contact them by email, fax, mail, and phone. Talking to companies, we must make sure to show them how our interests will benefit them.
See Also:
Ubuntu Marketing Team Campaign - Ubuntu In Stores
Ubuntu Marketing Team Campaign - Ubuntu Hardware Suppliers
Friendly Contact
Everyone should be able to get in touch with companies and just say what you want. For example, you could go to a computer retail store and ask them about supporting Ubuntu, then show off your own computer running it. They'll like the spinning cube 
There are also suggestion boxes that should be taken advantage of at every opportunity. For example: Dell's IdeaStorm
Complaint Letters
Tips:
- State your purpose
- State your reasons
- State the importance
- State your request
- Ask for a reply
Complaint letters can be used to ask companies to listen to our requests aside from complaining about things like service and broken products.
View an example from the consumerist.
Executive Customer Service
Executive customer service staff have the power to pull strings and most large companies have them. Here's how to get through to them
- For public companies, pull up the profile page in Google Finance and the corporate office should be listed under "Company Facts".
- Call the corporate office.
- Ask for a transfer to the office of the CEO.
- You will likely get an exec. assistant but that's good. Voice mail is ok, too.
- Give succinct summary and make your point.
- Remain polite.
You should get the phone call from someone on the executive service team within a day or so.
The Hardball Route
This is probably unnecessary, and isn't recommended for most things.