We'd also like to write an essay someday on how most porn scenarios are built around the same handful of tried-and-true archetypes: nurse and patient, schoolgirl and teacher, housewife and handyman, and so on. Ponder the following examples from some pay site preview galleries for now while we continue our research.
Nurse & Patient (TGP/preview gallery)
Dirty Teachers & Naughty Students (TGP/preview gallery)
Housewife & Handyman