What words/phrases are bleeped for different ratings?

"While the MPAA does not publish an official list of what exact words,
actions, and exposed body parts are used to determine a movie's
rating, some details have nonetheless been made available:

if a film uses 'one of the harsher sexually-derived words' (such as
f**k) once, it remains eligible for a PG-13 rating, provided that the
word is used as an expletive and not in a sexual context;
 
if such language is used more than once, or once if in a sexual
context, it usually receives an R rating."

http://www.wordiq.com/definition/MPAA_film_rating_system