There are several websites that offer free business letter templates, including a generalized template provided on Samplewords. This simple Microsoft Word template provides suggestions on what to include in each section of the letter.
For more specific business letter formats, visit the Writing Help Central website. Select from several options in the two main categories of business-to-business and business-to-customer letters, including introductions, contracts and invitations. On Vertex 42's website, there are several business letter template options, including a customizable version and a more specific letter of introduction. This site also provides recommendations on the most appropriate and effective use of each template.