How do I wire a new ceiling light with power to the ceiling and 3-way switches?
What you have is power to the ceiling, and 3-Way switches.

My best guess, is to wire the two blacks together in the ceiling, with a wire nut.
One of the whites should be marked.  This will go to the Black of the fixture.  The other white wire should go to the white of the fixture.  And then connect the ground.

So the path will be  Panel Hot -> Black wire -> [ Switch Common -> Switch Travellers ->Switch common -> ] WHITE -> Light -> Panel Neutral.

the stuff in Brackets [] is in the wall, and you won't see it.

See this http://diy.blogoverflow.com/2012/01/poles-and-throws/ for more information on 3-way switches.