Given that the consensus still seems to be that thank you cards are a vital after a job interview, Calgary Public Library customers often ask staff for books or magazine articles that can offer guidance on how to write such letters. Books such as Hire Me, Inc: Interviews The Get Offers and The Advice of a Headhunter offer strategies for writing meaningful letters when "going for the close" in trying to secure a job. They also discuss whether email or hand written notes are the best options in trying to make your letter stand out from the crowd.
A recent article in the Globe and Mail had a nice summary of the four main elements you should include in your thank you letter. The author, a career coach, stresses that such letters should be much more than notes to say "Thank you for the opportunity to meet you."
Staying on the Radar After The Job Interview