At times it is good to appreciate what one person or a group of people have done for us. This could be due to the help or assistance they offered during a hard time or in making a certain event or ceremony successful. It might be a case of you appreciating your boss or a boss appreciating his/her employees for a job well done or it might be an appreciation of a client or one for a job referral. An appreciation letter or a certificate of appreciation would help you relay this in a better way that is more personal in nature. This site offers you with a variety of sample appreciation letters as well as a certificate.