I know that the F-16 (F-16I and Block 50/52/60 models) have conformal fuel tanks standard now on top of the wing/fuselage area. The Silent Eagle model of the F-15E proposed by Boeing for South Korea, and other F-15E customers had them added. The F-18E (Superhornet) has demoed a set recently.
But on older aircraft, how common were conformal fuel tanks? Or have they always been drop tanks before?