Company giving may be seen as the least important source of funding, as many companies only give to well known charities. However, it is always good to build a rapport with companies in the local area and show the value that your charity can bring to a local business. Asking local businesses for donations or sponsorship can help to raise the company's profile and demonstrate that they are showing positive social responsibility within the local community.
Unsolicited appeals for sponsorship and donations are received by companies on a daily basis. It is always worth doing your research about companies who give to charity and the types of charities they give to.
Your local library will contain lots of information on company giving and the causes that each company is sympathetic to. One book to look out for is The Guide to UK Company Giving.
A recent report by CAF (Charities Aid Foundation) found that companies had not changed their charitable aims in recent years. They also found that charities find it hard to identify the decision maker within a company, so it's always worth doing your research.