*Please consult OptimalLetter for more ideas.
You should send a thank you letter after you have had an interview. In fact, mail it right after the interview, that very day. It should be brief, personalized and restate your interest. Follow this three paragraph procedure.
Sending a thank you letter after the interview will reinforce in the interviewer's mind just how serious you are about the position. This can separate you from the other candidates.
Contact Kathy if you have questions.