A thank you card for those who interviewed you and for the residents and chief residents who have taken you for a hospital tour or for dinner would be very nice. Ask the program coordinator how to proceed with this, she will usually tell you, give me the cards and I will hand it to the recipients.
Make the cards specific for each one. Thank you for taking me into amazing hospital tour, thank you for the informative interview, ...etc
If you don't want to do the cards, you can do emails but cards are more powerful.
Now, if you are really interested in that program then it's a good idea to contact them again. This can be done in two ways:
1) Second Look;
Asking for a second look would really show your interest and would also really help you determine if you really like this program or not. Asking for second look should be asked soon after the interview (I'd say within 2 weeks) but don't be pissed off if they reject your request, some programs do not allow second looks, that's normal.
2) I will rank you;
An "I will rank you" communication is a good hint from your side that you are interested in the program. Try not to be too much exaggerating and be realistic. For example a crap program in NY, it's not wise to tell them that they are the best program ever and that you will rank them number 1, that's so an obvious lie and they won't believe you. On the other hand, if you really like a program you can tell them that you will rank them number 1. The "I will rank you" communication usually comes late, shortly before the ranking time in February 2013.
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