How to interview a programmer?

Hey. It is interesting to know your opinion or advice. On such a simple question, as the head of the IT department \ personnel manager, hire a competent php \ ruby ​​\ c ++ \ etc programmer, not knowing the subject at a sufficient level. What questions to ask, what to pay attention to first of all, we consider the purely professional side. It is clear that it is necessary to look at the resume, to look at experience, participation in specialized forums. Please do not send "to the agency."

Have you encountered such a problem as you have solved?