My Top Recommendation

If you want to write a letter fast, I highly recommend that you use the templates provided in 3001 Business & Sales Letters because they have (as the name suggest) 3001 Business & Sales Letters templates. This award winning software has by far the most comprehensive list of templates. Here is a list of the templates they have ordered by categories.

As I can see it, the templates will cover every conceivable business situation. With this product, all you have to do to be good at Writing Business Letter is to cut, paste and do a little bit of modifications. It even gives you phrases (see screen shot) when you need it to help you construct sentences. See the following business sample letter to see how this program will help you write any letter you want. It is by far the best value for your money. 

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You might also try the new 4001 Business & Sales Letters