Trivia: best-selling book?

With apologies for the utterly trivial nature of the question, but anyway:
does anyone know what Foucault's best-selling book in English (apart from
the recent selections from Dits et Ecrits) is at the moment?  I would've
sworn it was HS1, but I have a friend in psychology who says that
Power/Knowledge is the one she sees everywhere.

Well, maybe not so trivial--it's always interesting to know which way the
Foucault barometer is swinging (as we all know, everyone in academia
loves Foucault, except for those who hate him, which is also everyone)....

Matthew

 ---Matthew A. King---Department of Philosophy---York University, Toronto---
       "We should consider every day lost on which we have not danced 
                               at least once."
 --------------------------------(Nietzsche)--------------------------------