New York is proud and vocal about its open data initiatives, but—curiously—does not make readily accessible one important data set: a list of rent stabilized apartments. This data set certainly exists somewhere, if not in the open, because New York's Department of Finance certainly knows which landlords it gives tax breaks to (rent stabilization is partly a function of whether landlords receive tax breaks for making repairs to old units).
This sketch grew out of my frustrating search for rent stabilization data. In the process of trying to find out whether my own apartment was rent stabilized, I was struck by how many useless data sets I found instead of the one I was actually looking for.
More detailed notes and resources here.