http://www.4hb.com/letters/

http://www.effective-business-letters.com/

http://www.effective-business-letters.com/500-Free-Business-Letters.html

http://www.writinghelp-central.com/sample-letters-business.html

http://www.englishclub.com/business-english/correspondence-samples.htm

https://owl.english.purdue.edu/sitemap/   (กด Confrol+F พิมพ์คำว่า letter)

http://www.thewritesource.com/studentmodels/     (กด Confrol+F พิมพ์คำว่า business letter)