Actually, most do NOT require a chairman's letter. I was an applicant last year, and only one program required such a letter (out of 30 applied to). I can't remember which one it was though, sorry! A few of us split up our lists of programs and called each individually to find out the requirements. We asked about # of LOR required, yes/no chairman's letter, MCAT, SAT (most laughed at this question), chief resident letter, etc...