Adore this Zac Posen dress that the lovely Sarah Chalke sported last week.  I think it is the perfect combination of professional and sexy.  Not that you would wear it to the office, but you definitely could wear it to a fancy shindig where work is discussed, like Sarah did.  The dramatic open keyhole has the opposite effect of a plunging neckline, as in cleavage is not the goal, but showing just enough skin is.  Make this look work for you:

Here’s a silk dress by Geren Ford that has the same idea.  Cinch with a similar tone but constrasting braided belt - I would put the buckle in the back to keep the front lines more smooth.  Finish off with a sweet peep toe pump and you are ready to take on this naughty but nice look!