Famous Artists School
I like the 1960s comics that feature the above Famous Artists School advertisement on their back covers. I never gave one second's thought to clipping the coupon and sending my name in to that school though (whereas I did think for a bit about applying to the Joe Kubert School the year it opened, as I previously mentioned over here).
The famous artists (that's them down below) who developed the curriculum for the F.A.S. correspondence courses left behind an archive of material that only recently has been directed to The Norman Rockwell Museum. You can read the full details over in this New York Times article from last month.