Depends on your definition of "posed"

• Mischa Barton: in addition to finding it impossible to keep her clothing on in public, Mischa did extensive nude scenes in Closing the Ring.
  
• Mena Suvari: in addition to her very famous topless scene in American Beauty, she did nude scenes in Stuck, and has been caught topless and nearly bottomless at the beach.
  
• Reese Witherspoon: topless in Twilight.
  
• Anne Hathaway: topless in two films. One is Brokeback Mountain, of course, and the other is a more obscure effort named Havoc. Hathaway also famously stirred up controversy by wearing a completely see-through top in public, making her virtually topless.
  
• Vanessa Minnillo: has worn a completely transparent top in public.
  
• Rachel McAdams: did a skinny-dipping scene in My Name is Tanino